Files with the .MAN extension contain commands or the contents of an app instruction manual for systems from the UNIX family. It is documentation that can be browsed in the operating system shell using the MAN command. It is saved in pure text form, and so it can be opened and edited using a regular text editor.

This extension is, however, usually not used for manual files, which instead have extensions in the form of numbers from 1 to 8 to signify the category of the file, with the command name or the manual topic being used as the file name.