The Publish/Subscribe pattern (often abbreviated as Pub/Sub) is a communication pattern in software development that enables loose coupling between components or systems. It involves two main actors: the Publisher and the Subscriber.

• Publisher: Responsible for generating and publishing messages or events. A Publisher sends messages to a central location, the Message Broker or Pub/Sub system.

• Subscriber: Registers for specific types of messages or topics it wants to react to. A Subscriber receives messages published by the Publisher and forwarded by the Message Broker to the respective subscribers.

The key concept in the Pub/Sub pattern is that the Publisher doesn't send messages directly to specific recipients but rather to a central intermediary system. This system stores messages and then distributes them to all Subscribers interested in the corresponding topic or type of message.

The pattern enables decoupled, scalable, and flexible communication between different parts of an application or between different applications. It's used in various systems and technologies, including messaging brokers, cloud platforms, IoT (Internet of Things), real-time analytics, and other scenarios requiring flexible message delivery.