There is only one file type that uses the .LIBRARY-MS extension:
Windows Library Description File
Operating system file introduced with Microsoft Windows 7; appears as a subfolder within the Libraries folder in the left side panel of the Windows Explorer; includes references to one or more folders that can be browsed when the library is opened.
LIBRARY-MS files are used for creating virtual folders with collections of similar files. For example, Windows 7 creates Documents, Music, Pictures, and Video libraries by default. You can create custom libraries by right-clicking the Libraries folder and choosing. When you open the new library, Windows provides an button that you can click to add folders to the library.
Updated: May 27, 2011