Solution Folders

Solution Folders: "Visual Studio
Solution Folders
If you are working with a solution that contains numerous projects, you can use Solution Folders to organize related projects into groups and then perform actions on those groups of projects. To organize and work with a solution, you can:
Create Solution Folders and move or add projects to them. Solution Folders can be nested to create greater organizational structure.
Add, delete, or rename Solution Folders at any time, if the organizational requirements of the solution change.
Unload all projects in a Solution Folder to make them temporarily unavailable for building.
Collapse or hide entire Solution Folders so that you can work more easily in Solution Explorer. Hidden projects are built when you build the solution.
To work with a group of projects in a Solution Folder as you develop your application, you can:
Apply the same policy to all the projects by setting the Policy File property for the Solution Folder.
Build or rebuild all the projects. The projects are built in the order specified by the project dependencies.
Information about the Solution Folders, including the projects and solution items that they contain, is stored in the solution file (.sln)."