There is only one file type that uses the .NOMEDIA extension:
Android No Media File
A NOMEDIA file is a file stored on an Android mobile device, or on an external storage card connected to an Android device. It marks its enclosing folder as having no multimedia data so that the folder will not be scanned and indexed by multimedia players or file browsers' search function. NOMEDIA files have no filename prefix and are simply named .nomedia.
The use of NOMEDIA files helps boost performance by excluding folders that do not need to be scanned. For example, a folder that has thousands of songs or images can be excluded. NOMEDIA files can also be used to hide ads featured in free apps when placed in the same directory of the ad. Many Android audio and video players, as well as image browsers (Gallery, MP3 Player, Video Player, etc.), recognize NOMEDIA files.
NOTE: NOMEDIA files can be managed by utilities such as StudioKUMA .nomedia Manager or Nomedia.
Updated: June 10, 2020