Application pool

1. An application pool is a group of one or more URLs that are served by a worker process or set of worker processes. Any Web directory or virtual directory can be assigned to an application pool. Every application within an application pool shares the same worker process.

   isolatation:

   Application pools allow you to isolate your applications from one another, even if they are running on the same server. This way, if there is an error in one app, it won't take down other applications.

   Additionally, applications pools allow you to separate different apps which require different levels of security, reliability, and availability.

   Main Point to Remember: 

   1. Isolation of Different Web Application 
   2. Individual worker process for different web application 
   3. More reliably web application 
   4. Better Performance