What are HTTP Handlers?

HTTP handlers are the .NET components that implement the System.Web.IHttpHandler interface, they can act as a target for the incoming HTTP requests and can be called directly by using their file name in the URL.

HTTP handlers implement the following two methods:
1) ProcessRequest: called to process http requests and
2) IsReusable which indicates whether this instance of http handler can be reused for fulfilling another requests of the same type.