A publish-subscribe system is a messaging pattern where senders, known as publishers, send messages without needing to know who will receive them. Instead of direct communication, messages are categorized into topics, allowing multiple receivers, called subscribers, to express interest in specific topics. This decouples the publishers from the subscribers, enabling more flexible and scalable communication. In this system, when a publisher sends a message, it is distributed to all subscribers interested in that topic. This model is commonly used in various applications, including real-time notifications, news feeds, and event-driven architectures, facilitating efficient information sharing among multiple users or systems.