Visual Studio Solution
[MSDN: http://msdn.microsoft.com/en-us/library/bb165922(VS.80).aspx]
Overview of Solutions
A solution is a grouping of one or more projects that work together to create an application. The project and status information that pertain to the solution are stored in two solution files, a text-based solution (.sln) file and a binary solution user option (.suo) file. These files are similar to the group (.vbg) files that were used in earlier versions of Visual Basic, and the workspace (.dsw) files and user options (.opt) files that were used in earlier versions of Visual C++.
Solution (.sln) File
The .sln file contains text-based information the environment uses to find and load the name-value parameters for the persisted data and the project VSPackages it references. When a user opens a solution, the environment cycles through the preSolution, Project, and postSolution information in the .sln file to load the solution, projects within the solution, and any persisted information attached to the solution.
Solution files (with the .sln file extension) are used to group related projects together and are primarily used to control the build process. You can use solutions to control build dependency issues and control the precise order in which contained projects are built.
Note:
1. Project dependencies are included in .sln file.
2. A project can be part of one or more solutions but solutions can't be included within other solutions.
Solution User Options (.suo) File
The solution user options (.suo) file is a structured storage, or compound, file stored in a binary format. You save user information into streams with the name of the stream being the key that will be used to identify the information in the .suo file. What included in .suo file are below things (breakpoints, source control info like P4 server info and bookmarks are inside it):
The .sln file can be shared between developers on a development team. The .suo file is a user-specific file, and cannot be shared between developers.