HTTP Handlers: An ASP.NET HTTP handler is the process that runs in response to a request that is made to an ASP.NET Web application. The most common handler is an ASP.NET page handler that processes .aspx files. Below are the different HTTP Handlers available in ASP.NET.
HTTP Modules: An HTTP module is an assembly that is called on every request that is made to your application. HTTP modules are called as part of the request pipeline and have access to life-cycle events throughout the request.