Project and Solution File Types
Visual Studio supports many file types. In a particular installation, the installed components determine which file types are supported. This topic lists solution and project file types that are supported in some typical installations. For information about other file types, search by using the file name extensions for each type.
Visual Studio uses two file types (.sln and .suo) to store settings specific to solutions. These files, known collectively as solution files, provide Solution Explorer with the information it needs to display a graphical interface for managing your files. They allow you to concentrate on your projects and final goals rather than on the environment itself each time you return to your development tasks.
Visual Studio Solution
Organizes projects, project items and solution items into the solution.
Solution User Options
Keeps track of user-level customizations you have made Visual Studio, such as breakpoints.