Worker Process (w3wp.exe)? - ablealias/asp.net GitHub Wiki
The Worker Process (w3wp.exe) runs ASP.NET applications within IIS. All ASP.NET functionality runs under the scope of the Worker Process.
When a request comes to the server from a client, the Worker Process is responsible for generating the request and response. Its also maintains the InProc session data. If we recycle the Worker Process, we will lose its state.
Application Pool: This is one of the most important things that you should create for your own application in a production environment.
Application Pools are used to separate sets of IIS Worker Processes that share the same configuration. Application Pools enable us to isolate our web application for better security, reliability, and availability.