System.IObserver

Defines a provider for a push-based notification.
link - learn.microsoft.com/en-us/dotnet/api/system.iobserver-1?view=net-5.0
link - learn.microsoft.com/en-us/dotnet/standard/events/how-to-implement-an-observer
The observer design pattern enables a subscriber to register with and receive notifications from a provider.
It is suitable for any scenario that requires push-based notification.