APE

APE is the file extension of Monkey's Audio files. Monkey’s Audio is a file format for audio data compression. Being a lossless compression format, Monkey’s Audio does not remove information from the audio stream, as lossy compression formats such as MP3, AAC, and Vorbis do.

Like other methods of compression, the main advantage of using Monkey’s Audio lies in a reduction of bandwidth and/or a reduction in storage requirements. A digital recording (such as a CD) encoded to Monkey’s Audio format can later be decompressed into an identical copy of the original audio data. Like the Apple Lossless format, files encoded to Monkey’s Audio are typically reduced to about half of the original size.

Monkey’s Audio is a proprietary software, it is often too slow to decode on portable audio devices, and it has limited/problematic support on software platforms other than Windows. There are alternatives that provide the user with more freedom and support for more platforms, such as the FLAC formats.

Wikipedia