Acronym for Portable Music Player.
PMP describes any digital portable music player which allows users to download or save digital music files (in MP3 format) from their computer to play on their PMP. Some examples of a PMP would be the iPod, iRiver, Rio Karma, and the NOMAD to name a few.
See also The Difference between an iPod vs. MP3 Player in the Did You Know…? section of Webopedia.