SignalR is a library that makes it extremely easy to add real-time communication to your applications. This means your servers and their clients can push data back and forth to each other in real time. This opens up a whole new world of possibilities for applications that simply weren’t feasible in the past, and allows you to interact with your users on a whole new level.
ASP.NET SignalR is a library for ASP.NET developers that simplifies the process of adding real-time web functionality to applications. Real-time web functionality is the ability to have server code push content to connected clients instantly as it becomes available, rather than having the server wait for a client to request new data.