ASP.NET defines a few directories with special meanings.
Bin Contains all the precompiled .NET assemblies usually DLLs
App_Code Contains source code files that are dynamically compiled for use
App_GlobalResources stores global resources
App_LocalResources resources are accessible for their dedicated page only
App_WebReferences Stores references to web services that the web application uses.
This includes WSDL files and discovery documents.
App_Data reserved for data storage
App_Browsers browser definitions stored in XML files
App_Themes themes used by the web application