A channel in ASP.NET is a new feature introduced in .NET Core 2.1 that provides a high-performance, scalable way to communicate between different parts of an application.

Channels enable efficient message-passing between different components of an application that are executing concurrently. It provides a way to pass data from one part of the application to another without the need for explicit synchronization or locking.

In the context of ASP.NET, channels can be used to create real-time applications, such as chat rooms or stock tickers, where data is constantly being updated and transmitted between the server and client in real-time.

Channels are implemented using the System.Threading.Channels namespace, which provides a variety of channel types with different performance characteristics, such as bounded and unbounded channels, single and multiple readers and writers, and different buffering strategies.

Using channels in ASP.NET can result in better performance and scalability compared to other traditional methods of inter-component communication, such as events or callbacks.