Application Pages Vs Site Pages Vs Custom aspx Pages

Definition:

 

Application Pages : An application page is deployed once per Web server and cannot be customized on a site-by-site basis.

Site Pages : These are pages that make up the site interface and are specific to one site or site collection.

Custom aspx Pages : These are the pages that are added via feature and\or solution package for a specific purpose or function.

Developers usually deploy them in Layouts folder.

Storage:

Application Pages : They stay in 12 hive folder structure, mostly under layouts folder and aare

used by all the sites and site collections for that server.

Site Pages : They mostly get stored in the content database of the site collection.

Custom aspx Pages : If deployed in Layouts folder the remain uncustomized thus do not get stored in the Content database.

Code Behind :

Application Pages : They do support code behind and inline scripts.

Site Pages : They do not support code behinds. We can only add WebPart zones to the site pages.

Custom aspx Page : They can have a code behind and inline scripts. The code behind file is not deployed though.

Look and Feel :

Application Pages : They do not inherit websites current master page. They will always inherit from application.master.

Site Pages : They inherit the custom look and feel of the site.

Cutsom aspx Pages : They do inherit the Look and feel of the site they are deployed in. You will have to specify the url of the Custom master page while deploying them.