Azure Web Pub Sub Service is a real-time messaging service that uses websockets. It allows building real-time web applications by facilitating high-volume requests and simultaneous connections. The service is currently in preview. Key concepts include services, servers, clients, groups, and messages. Servers generate access tokens and can create groups. Clients connect using websockets and standard APIs to send and receive messages within groups. The service can also be used with Azure Functions for event-driven programming.