These concepts clarify the API's messaging resources:

  • Topic. An ordered collection of messages.

  • Message block. A message or group of messages sent from a single topic.

  • Message. An individual object stored in a topic.

  • Consumer group. Multiple subscribers sharing a single subscription. All group members receive alternating messages, with each message sent only to one group member. It's most commonly used for load balancing.

  • Retained message. It's an MQTT message automatically sent to the subscriber at the moment of subscribing. It is most commonly used for configuration or status updates.