What is Pub/Sub messaging?

Pub/Sub (Publish-Subscribe) messaging is a messaging pattern where senders of messages (publishers) do not program them to be sent directly to specific receivers (subscribers). Instead, published messages are categorized into channels without knowledge of what (if any) subscribers there may be. Subscribers express interest in one or more channels and only receive messages that are categorized in those channels. This allows for decoupling of applications, increased scalability, and more dynamic system architectures. It's commonly used for event notifications, data streaming, and real-time updates.