.mp+

A .mp+ file is a Musepack music file, a popular high quality lossy compression that offers higher audio quality than MP3. Nowadays Musepack audio files generally have the extension .mpc, but lots of files with the extension .mp+ still float around file sharing networks. Musepack is based on the MPEG-1 Audio Layer 2 standard (MP2), but includes many improvements. It is believed by audiophiles to be one of the highest quality lossy compressions available for music.

Foobar 2000 is an excellent software audio player that supports Musepack. If you wish to burn Musepack audio files as an audio CD, you can download a plugin for MPC files for Nero Burning Rom here.