In publish-subscribe messaging, message producers and consumers are known as publishers and subscribers.

The central concept in the publish-subscribe messaging is a destination called a topic. Message publishers send messages of specified topics. Clients that want to receive that type of message subscribe to the topic.

The publishers and subscribers never communicate with each other directly. Instead, they communicate by exchanging messages through a message Broker.

Publishers and subscribers have a timing dependency. Clients that subscribe to a topic can consume only messages published after the client has created a subscription. In addition, the subscriber must continue to be active to consume messages.

The messaging APIs relax this dependency by making a distinction between durable subscriptions and non-durable subscriptions.