AUP, Audacity Project File (.aup)
The AUP Audio file format
AUP is a file format created by Audacity. It is saved in an XML format. The file is basically a reference to various audio files as well as the sound edits applied on them. AUP files are used by the Audacity program to save edited audio files.
Technical details of AUP files
AUP files are saved in a corresponding folder named after the project name chosen by the user, where the AUP file refers to the project file itself. The folder is used to save chunks of audio data in an optimized format. These files can only be opened using the Audacity software bundle.