Possible Duplicate:
ASP.NET: Web Site or Web Application?
Difference between 'Web Site' and 'Project' in Visual Studio
In Visual Studio 2010 what is the difference between a web site (created using File->New->Web Site) and any of the numerous web application projects?
MSDN covers Web Application Projects versus Web Site Projects in their documentation.
It highlights the differences between web app and web site projects such as: