An EXO file is a video file saved in the EXO format and is used by the YouTube application for Android. It stores a chunk, or segment, of a video downloaded from the YouTube app for offline playback. EXO files are automatically pieced together with other EXO chunks of the whole video by the YouTube app in order to be played.

The EXO format is only supported by the YouTube Android app available in select countries, such as India, the Philippines, and Indonesia. When you download a video from the YouTube app to be played offline, the video is downloaded in multiple chunks with the .exo extension, then they are compressed and encrypted. This is done to prevent videos from being shared illegally. When the user selects an EXO file for playback, the video is decrypted and reassembled by the YouTube app.