MNU files are customization files for the Adobe Photoshop image-editing software. In it, data for own Menkonfigurationen be stored, such as which Meneintrge to be displayed at all, or whether a menu should be highlighted.
For example, a new CS5.Mnu is included with Photoshop CS 5, which highlights all new menu options. There are also presets like 'Film and Video' or 'Image Analysis'. To use a MNU file, you can usually simply double-click it or reach it under 'Window-> Workspace. If a menu setting should appear here, the MNU file must be copied to 'Preferences / Customize' in the Photoshop main directory.
You can create or change your own menus under 'Edit-> Mens-> Tabs (Men)'. There is no way to load an MNU file. For a menu adjustment to be selected here, the corresponding MNU file must be in the correct directory (see above).
Especially useful are MNU files to save your own customization (for example, for a new installation) or to transfer them to another (work) computer.