What are the differences between Web Sites and Web Applications?

Default website project model uses the directory structure to define the contents of the project.

 In this model, there is no project file and all files in the directory are part of the project.

Also you can directly edit and run the content of the project without doing any compile.

Web application project, the files that are explicitly referenced in the solution's project file are the only ones that are part of the project. These files are displayed in Solution Explorer and they are the only files that are compiled during a build.

Edited files are created files can run only after compile.