What is the difference between iisreset, recycle, refresh and restart?

iisreset

iisreset will stop and start the World Wide Web Publishing Service. This, of course, applies to all of your application pools.

Recycle application pool

A process being created for each application pool. This process will handle requests for all websites associated with it. When you recycle an application pool, IIS will create a new process (keeping the old one) to serve requests. Then it tries to move all requests on the new process. After a time-out the old process will be killed automatically.

You usually recycle your application pool to get rid of leaked memory. You might have a problem in your application if this needs to be a regular operation. It is recommended to have a scheduled recycle.

Restarting a website

As for restarting a website, it just stops and restarts serving requests for that particular website. It will continue to serve other websites on the same app pool with no interruptions.

If you have a session oriented application, all of the above will cause loss of session objects.

Refreshing IIS or a website

Refreshing a website has no effect on the service/process/website and is merely a UI command to refresh the tree-view. For example you have added a directory that you don't see in the management console. Then refreshing the website will show the new directory in the treeview.