1646 IoT Glossary: Q-Z
Essential IoT Terms from QoS to 6LoWPAN
This is Part 3 of the IoT Glossary, covering terms Q-Z. See also:
- IoT Glossary Index - Overview and quick navigation
- Glossary A-F - ACL through Frame
- Glossary G-P - Gateway through Publisher
1646.1 Learning Objectives
After reviewing this section, you should be able to:
- Define key IoT terms from Q to Z with technical accuracy
- Understand quality of service levels and their implications
- Distinguish between wireless protocols (Zigbee, Z-Wave, Thread, Matter)
- Identify appropriate database technologies for time-series IoT data
1646.2 Q
1646.2.1 QoS (Quality of Service)
Definition: A set of mechanisms that control and guarantee network resources and delivery characteristics, particularly message delivery guarantees (at-most-once, at-least-once, exactly-once).
In simple terms: Delivery guarantees - like choosing between regular mail, tracked delivery, or registered mail depending on how important your package is and how sure you need to be it arrives.
Common confusions: - MQTT QoS (0, 1, 2) refers to message delivery, not network performance - Higher QoS means more overhead and latency
Related terms: At-most-once, At-least-once, Exactly-once, Acknowledgment
Synonyms: delivery quality, service level
1646.3 R
1646.3.1 REST (Representational State Transfer)
Definition: An architectural style for web services using HTTP methods (GET, POST, PUT, DELETE) to perform CRUD operations on resources, emphasizing stateless communication and uniform interfaces.
In simple terms: Web API design principles - a common way to build APIs where URLs represent things (resources) and HTTP methods represent actions (get, create, update, delete).
Common confusions: - REST vs. RESTful - REST is the style, RESTful describes APIs following REST principles - Not all HTTP APIs are RESTful (many only use POST)
Related terms: API, HTTP, Microservices
Synonyms: REST API, RESTful API
1646.3.2 Retry
Definition: The practice of automatically re-attempting a failed operation, typically with backoff strategies and maximum attempt limits to handle transient failures gracefully.
In simple terms: “Try again” - when something fails, automatically attempt it again (perhaps after waiting) because many failures are temporary and succeed on retry.
Common confusions: - Retries without backoff can overwhelm systems (thundering herd) - Not all operations should be retried (only transient failures)
Related terms: Backoff, Idempotency, Circuit Breaker
Synonyms: retry mechanism, automatic retry
1646.3.3 Routing
Definition: The process of selecting paths in a network for traffic to flow, using algorithms and routing tables to determine the best path for data to reach its destination.
In simple terms: Finding the best route - like a GPS navigating traffic, routers determine the best path for data to travel from source to destination through the network.
Common confusions: - Routing vs. switching - routing works between networks (Layer 3), switching works within networks (Layer 2) - Static vs. dynamic routing have different use cases
Related terms: Mesh, Gateway, Packet
Synonyms: packet routing, path selection
1646.4 S
1646.4.1 Sampling
Definition: The process of converting continuous signals into discrete values at regular intervals, with sampling rate determining how often measurements are taken.
In simple terms: Taking periodic snapshots - instead of continuous recording, take measurements at regular intervals, like checking temperature every minute instead of watching a thermometer constantly.
Common confusions: - Sampling rate must be at least 2x highest frequency (Nyquist theorem) - Higher sampling rates produce more data but may not add value
Related terms: ADC, Time Series, Aggregation
Synonyms: data sampling, signal sampling
1646.4.2 Schema
Definition: A formal description of data structure defining field names, types, constraints, and relationships, used to validate data and ensure consistency across systems.
In simple terms: A data template - specifies what fields data should have and what types they should be, like a form that defines required fields and their formats.
Common confusions: - Schema-on-write vs. schema-on-read have different flexibility/reliability tradeoffs - Schema evolution must be managed carefully to maintain compatibility
Related terms: JSON, Protobuf, Serialization
Synonyms: data schema, data model
1646.4.3 Sensor
Definition: A device that detects and measures physical properties (temperature, light, motion, pressure) and converts them into electrical signals that can be processed by electronic systems.
In simple terms: The eyes and ears of IoT - devices that measure the real world and report what they sense, like a thermometer that tells a computer what the temperature is.
Common confusions: - Sensor vs. transducer - sensors measure, transducers convert energy forms (sensors are a type of transducer) - Sensor accuracy vs. precision are different characteristics
Related terms: Actuator, ADC, Telemetry
Synonyms: detector, transducer
1646.4.4 Serialization
Definition: The process of converting data structures or objects into a format suitable for storage or transmission, enabling reconstruction of the original structure later (deserialization).
In simple terms: Packing for shipment - converting complex data into a flat format that can be sent over a network or saved to disk, then unpacking it at the destination.
Common confusions: - Serialization format affects size, speed, and compatibility (JSON vs. CBOR vs. Protobuf) - Deserialization must handle malformed or malicious data safely
Related terms: JSON, CBOR, Protobuf, Payload
Synonyms: marshalling, encoding
1646.4.5 Serverless
Definition: A cloud computing execution model where the cloud provider dynamically manages server allocation, charging only for actual execution time, abstracting infrastructure management.
In simple terms: Computing without managing servers - write code that runs when needed without worrying about servers, scaling, or paying for idle time, like renting a taxi versus owning a car.
Common confusions: - Serverless still uses servers, you just don’t manage them - Cold start latency can affect time-sensitive applications
Related terms: Cloud, Microservices, Platform
Synonyms: Function as a Service (FaaS), Lambda
1646.4.6 Sigfox
Definition: A proprietary LPWAN technology using ultra-narrowband modulation for very low-power, low-throughput IoT communication, operating a global network with subscription-based service.
In simple terms: A global IoT cell network - like a phone network just for simple sensors, covering the world with one subscription for devices that only send tiny amounts of data.
Common confusions: - Sigfox is network-as-a-service (you don’t deploy your own infrastructure) - Very limited message size (12 bytes) and daily message count (140)
Related terms: LPWAN, LoRaWAN, NB-IoT
Synonyms: none common
1646.4.7 SoC (System on Chip)
Definition: An integrated circuit that combines a processor, memory, I/O interfaces, and often wireless connectivity into a single chip, providing complete computing functionality for embedded systems.
In simple terms: An entire computer on one chip - everything from the processor to Wi-Fi radio combined into a single piece of silicon, making it easy to build small, integrated devices.
Common confusions: - SoC vs. microcontroller - SoCs typically include more features like wireless, microcontrollers are simpler - Examples: ESP32, Nordic nRF52, Raspberry Pi RP2040
Related terms: Microcontroller, GPIO
Synonyms: System on a Chip, integrated SoC
1646.4.8 SPI (Serial Peripheral Interface)
Definition: A synchronous serial communication interface using four wires (clock, data in, data out, select) for high-speed communication between a microcontroller and peripheral devices.
In simple terms: Fast wired communication - uses more wires than I2C but is faster, good for sensors and displays that need to transfer lots of data quickly.
Common confusions: - SPI vs. I2C - SPI is faster but needs more wires and individual select lines per device - SPI has multiple modes (CPOL/CPHA) that must match between devices
Related terms: I2C, UART, GPIO
Synonyms: four-wire serial bus
1646.4.9 Star Topology
Definition: A network topology where all devices connect to a central hub or coordinator, with all communication flowing through this central point rather than directly between devices.
In simple terms: Hub-and-spoke design - every device connects to one central point, like streets radiating from a town center. Simple but the center is a single point of failure.
Common confusions: - Star vs. mesh - star is simpler but less resilient, mesh has redundant paths - Wi-Fi networks typically use star topology with the access point as center
Related terms: Mesh, Routing, Gateway
Synonyms: hub topology, centralized topology
1646.4.10 Subscriber
Definition: A client in publish-subscribe messaging that registers interest in specific topics and receives messages published to those topics, without direct connection to publishers.
In simple terms: A listener - signs up to receive certain types of messages from the system, like subscribing to a newsletter to receive updates on topics you care about.
Common confusions: - Subscriber vs. consumer - essentially the same concept - Subscribers are decoupled from publishers (don’t know who’s sending)
Related terms: Publisher, Topic, Subscription, Broker
Synonyms: consumer, receiver, listener
1646.4.11 Subscription
Definition: A registration with a message broker expressing interest in receiving messages matching certain criteria (typically topic patterns), maintained until explicitly cancelled.
In simple terms: A standing order for messages - tell the broker “send me anything about topic X” and you’ll receive matching messages until you unsubscribe.
Common confusions: - Subscription vs. topic - subscription is the registration, topic is what you subscribe to - Durable vs. non-durable subscriptions persist (or not) across disconnections
Related terms: Topic, Subscriber, Filter, Wildcard
Synonyms: topic subscription
1646.5 T
1646.5.1 Telemetry
Definition: The automated collection and transmission of measurements from remote devices to receiving equipment for monitoring, including sensor readings, status information, and performance metrics.
In simple terms: Remote sensing data - the continuous stream of measurements sent from devices in the field back to a central system, like vital signs monitors sending patient data to nurses’ stations.
Common confusions: - Telemetry vs. commands - telemetry flows from devices, commands flow to devices - Telemetry vs. logs - telemetry is structured measurements, logs are event records
Related terms: Sensor, Time Series, MQTT
Synonyms: device telemetry, sensor data, metrics
1646.5.2 Thread
Definition: An IPv6-based mesh networking protocol designed for smart home devices, providing secure, reliable, low-power communication with no single point of failure.
In simple terms: Modern smart home mesh - a secure, reliable way for home devices to communicate in a mesh network, specifically designed to work with IPv6 and the Matter standard.
Common confusions: - Thread vs. Zigbee - Thread uses IP, Zigbee has its own network layer - Thread is a transport for Matter (they work together)
Related terms: Matter, Mesh, 6LoWPAN, Zigbee
Synonyms: Thread Group protocol
1646.5.3 Throughput
Definition: The actual rate at which data is successfully transferred over a network connection, typically lower than bandwidth due to protocol overhead, errors, and congestion.
In simple terms: Real-world speed - while bandwidth is the maximum theoretical capacity, throughput is how fast data actually moves in practice, accounting for all the overhead and delays.
Common confusions: - Throughput vs. bandwidth - throughput is achieved rate, bandwidth is capacity - Throughput varies based on conditions, bandwidth is a fixed characteristic
Related terms: Bandwidth, Latency
Synonyms: actual speed, effective bandwidth
1646.5.4 Time Series
Definition: A sequence of data points indexed by time, commonly used in IoT for recording sensor measurements, metrics, and events with timestamps for temporal analysis.
In simple terms: Data ordered by time - measurements collected over time, like temperature readings every minute, stored in time order so you can see trends and patterns.
Common confusions: - Time series databases are optimized differently than relational databases - Time series data often requires special handling for gaps and irregular intervals
Related terms: TSDB, Telemetry, Timestamp, Aggregation
Synonyms: temporal data, time-stamped data
1646.5.5 TimescaleDB
Definition: An open-source time series database built on PostgreSQL, combining full SQL support with time series optimizations for IoT, monitoring, and analytics workloads.
In simple terms: SQL-friendly time series database - handles sensor data efficiently while letting you use familiar SQL queries and benefiting from PostgreSQL’s ecosystem.
Common confusions: - TimescaleDB vs. InfluxDB - TimescaleDB uses SQL, InfluxDB has its own query languages - TimescaleDB is an extension to PostgreSQL, not a standalone database
Related terms: TSDB, InfluxDB, Time Series
Synonyms: none common
1646.5.6 Timestamp
Definition: A recorded point in time associated with data, typically expressed in a standardized format like Unix epoch time or ISO 8601, essential for ordering and correlating events.
In simple terms: A date-time stamp - marks when something happened, like the postmark on a letter, essential for knowing when sensor readings were taken.
Common confusions: - Timestamp precision matters (seconds vs. milliseconds vs. microseconds) - Timezone handling is crucial for distributed systems
Related terms: Time Series, Metadata, Telemetry
Synonyms: datetime, epoch time
1646.5.7 TLS (Transport Layer Security)
Definition: A cryptographic protocol providing secure communication over networks through encryption, authentication, and integrity verification, the successor to SSL.
In simple terms: The “S” in HTTPS - encrypts data in transit so eavesdroppers can’t read it, verifies server identity, and ensures data hasn’t been tampered with.
Common confusions: - TLS vs. SSL - TLS is the modern successor, SSL is deprecated - TLS works with TCP, use DTLS for UDP
Related terms: DTLS, HTTPS, Certificate, Encryption
Synonyms: SSL/TLS, secure sockets
1646.5.8 Token
Definition: A digital credential used for authentication or authorization, typically a string containing encoded information about identity and permissions with expiration time.
In simple terms: A digital key card - proves who you are and what you’re allowed to do, like a badge that gets you through certain doors for a limited time.
Common confusions: - Access tokens vs. refresh tokens serve different purposes - JWT (JSON Web Token) is one common token format
Related terms: Authentication, OAuth, Authorization
Synonyms: access token, bearer token, JWT
1646.5.9 Topic
Definition: A named channel or subject in publish-subscribe messaging systems that publishers send messages to and subscribers receive messages from, enabling message routing.
In simple terms: A message address or category - like a TV channel number, publishers broadcast to a topic and anyone tuned to that topic receives the messages.
Common confusions: - Topic hierarchy (sensors/temperature/room1) enables organized message routing - Topics are usually strings, not queues (messages aren’t stored by default)
Related terms: Publisher, Subscriber, Subscription, MQTT
Synonyms: channel, subject, message topic
1646.5.10 TSDB (Time Series Database)
Definition: A database optimized for storing, querying, and analyzing time-stamped data, featuring efficient compression, time-based indexing, and specialized query functions.
In simple terms: A database built for sensor data - specifically designed to handle millions of time-stamped measurements efficiently, with features like automatic data aging and time-based queries.
Common confusions: - TSDB vs. relational database - TSDBs optimize for time-based writes and queries - Examples: InfluxDB, TimescaleDB, Prometheus, QuestDB
Related terms: Time Series, InfluxDB, TimescaleDB
Synonyms: time series database
1646.6 U
1646.6.1 UART (Universal Asynchronous Receiver/Transmitter)
Definition: A hardware communication protocol for asynchronous serial communication between devices, using two wires (TX and RX) without requiring a shared clock signal.
In simple terms: Basic serial communication - the simplest way for two devices to talk to each other over wires, like an old-fashioned telegraph system for digital data.
Common confusions: - UART vs. I2C/SPI - UART is point-to-point and asynchronous, I2C/SPI support multiple devices - Baud rate must match between sender and receiver
Synonyms: serial port, RS-232 (related standard)
1646.7 W
1646.7.1 WebSocket
Definition: A protocol providing full-duplex communication channels over a single TCP connection, enabling real-time bidirectional data exchange between web clients and servers.
In simple terms: A two-way communication line - unlike HTTP where clients must keep asking for updates, WebSocket keeps a connection open so servers can push data instantly.
Common confusions: - WebSocket vs. HTTP - WebSocket is persistent and bidirectional, HTTP is request-response - WebSocket starts with HTTP upgrade, then switches protocol
Related terms: HTTP, MQTT, Real-time
Synonyms: WS, WSS (secure WebSocket)
1646.7.2 Wi-Fi
Definition: A family of wireless networking protocols based on IEEE 802.11 standards, providing local area network connectivity using radio frequencies in 2.4 GHz and 5 GHz bands.
In simple terms: Wireless internet - the most common way to connect devices to a network without cables, using radio waves to link devices to a router or access point.
Common confusions: - Wi-Fi vs. internet - Wi-Fi is the local connection, internet is what you access through it - Wi-Fi generations (4/5/6/6E/7) have different speeds and capabilities
Related terms: BLE, Zigbee, Bandwidth
Synonyms: Wi-Fi, 802.11, WLAN
1646.7.3 Wildcard
Definition: A special character in topic patterns that matches multiple topic levels, enabling subscribers to receive messages from multiple topics with a single subscription.
In simple terms: A pattern matcher - like using “*” to find all files in a folder, wildcards let you subscribe to groups of related topics at once.
Common confusions: - MQTT uses + (single level) and # (multi-level) wildcards - Different protocols have different wildcard syntax
Related terms: Topic, Subscription, Filter
Synonyms: topic wildcard, pattern matching
1646.8 Z
1646.8.1 Zigbee
Definition: A wireless mesh networking protocol based on IEEE 802.15.4 for low-power, low-data-rate applications, widely used in home automation and industrial control.
In simple terms: A mesh network for smart homes - devices form a web of connections where messages hop from device to device, creating reliable coverage throughout your home.
Common confusions: - Zigbee vs. Z-Wave - different protocols, incompatible, both used for home automation - Zigbee vs. Thread - Zigbee has its own network layer, Thread uses IPv6
Related terms: Z-Wave, Mesh, Thread, Matter
Synonyms: Zigbee, IEEE 802.15.4
1646.8.2 Z-Wave
Definition: A proprietary wireless mesh networking protocol operating in sub-GHz frequencies, designed for smart home automation with low interference and excellent building penetration.
In simple terms: Another smart home mesh - similar purpose to Zigbee but uses different radio frequencies that pass through walls better, with strictly controlled certification.
Common confusions: - Z-Wave vs. Zigbee - incompatible protocols, Z-Wave uses sub-GHz, Zigbee uses 2.4 GHz - Z-Wave is proprietary with mandatory certification, Zigbee is more open
Related terms: Zigbee, Mesh, Matter
Synonyms: none common
1646.8.3 6LoWPAN
Definition: IPv6 over Low-Power Wireless Personal Area Networks, an adaptation layer enabling IPv6 packets to be transmitted over IEEE 802.15.4 networks through header compression and fragmentation.
In simple terms: Shrinking IPv6 for tiny devices - makes full internet protocol (IPv6) work on constrained networks by compressing headers and splitting large packets.
Common confusions: - 6LoWPAN is an adaptation layer, not a complete protocol stack - Used by Thread and often paired with CoAP
Related terms: CoAP, Thread, MTU
Synonyms: IPv6 over LoWPAN
1646.9 Additional Reference Terms
1646.9.1 Cellular IoT
Definition: IoT connectivity using cellular networks (LTE-M, NB-IoT, 5G), leveraging existing mobile infrastructure for wide-area coverage and managed connectivity services.
In simple terms: Using cell phone networks for IoT - connecting devices through the same towers your phone uses, providing coverage almost anywhere without deploying your own network.
Common confusions: - Cellular IoT includes multiple technologies (NB-IoT, LTE-M, 5G mMTC) - Requires carrier subscription and SIM/eSIM
Related terms: NB-IoT, LTE-M, LPWAN
Synonyms: mobile IoT, cellular M2M
1646.9.2 IIoT (Industrial IoT)
Definition: Application of IoT technologies in industrial settings for manufacturing, energy, transportation, and other industrial processes, emphasizing reliability, safety, and interoperability.
In simple terms: IoT for factories and industry - connecting machines, sensors, and systems in industrial environments to improve efficiency, safety, and maintenance.
Common confusions: - IIoT vs. Industry 4.0 - IIoT is the connectivity, Industry 4.0 is the broader transformation - IIoT has stricter requirements for reliability and safety than consumer IoT
Related terms: OPC-UA, Modbus, Digital Twin
Synonyms: Industrial Internet of Things, Industry 4.0 IoT
1646.9.3 Real-time
Definition: System responses occurring within guaranteed time constraints, where data is processed and delivered with minimal delay to enable immediate action or feedback.
In simple terms: Instant response - systems that react immediately, like brake lights that come on the moment you press the pedal, not seconds later.
Common confusions: - Real-time doesn’t mean “fast” - it means “predictably within time constraints” - Hard real-time vs. soft real-time have different tolerance for delays
Related terms: Latency, DDS, WebSocket
Synonyms: real-time systems, low-latency
1646.9.4 Frequency
Definition: The rate at which a periodic signal oscillates, measured in Hertz (Hz), determining radio band allocation for wireless communication and signal characteristics.
In simple terms: How fast waves wiggle - measured in cycles per second, different frequencies are used for different purposes (2.4 GHz Wi-Fi, 915 MHz LoRa, etc.).
Common confusions: - Higher frequency generally means more bandwidth but less range/penetration - Different regions use different frequency bands (regulatory)
Related terms: Channel, Bandwidth, Wi-Fi
Synonyms: radio frequency, Hz
1646.10 Summary
This section covered 35 essential IoT terms from Q through Z plus additional reference terms:
| Category | Terms | Examples |
|---|---|---|
| Wireless Protocols | 7 | Sigfox, Thread, Wi-Fi, Zigbee, Z-Wave, 6LoWPAN |
| Messaging | 6 | QoS, Subscriber, Subscription, Topic, Wildcard |
| Data/Databases | 6 | Sampling, Schema, Serialization, Time Series, TimescaleDB, TSDB |
| Security | 3 | TLS, Token |
| Hardware | 4 | SoC, SPI, UART |
| Networking | 5 | REST, Retry, Routing, Star Topology, Throughput, WebSocket |
| Architecture | 3 | Sensor, Serverless, Telemetry |
| Reference | 4 | Cellular IoT, IIoT, Real-time, Frequency |
1646.11 What’s Next
Return to the IoT Glossary Index for an overview of all glossary sections, or navigate to specific sections:
- Glossary A-F - ACL through Frame
- Glossary G-P - Gateway through Publisher
For hands-on practice with these concepts, explore the Interactive Tools and Simulation Playground.