Moving Picture Experts Group Audio Layer 3 Uniform Resource Locator, or MP3 URL
m3u is a computer file format that stores multimedia playlists. It was originally implemented in Winamp, although it is now supported by many applications, including VLC media player, XMMS, foobar2000, JuK, RealPlayer, Windows Media Player, iTunes, QuickTime Player, Yahoo! Music Engine, JetAudio, RokuLabs SoundBridge, Spider Player, and PlayStation Portable.
"Hey, could you send me a copy of that tune?"
"Sure! Do you want the whole m3u of the album, or just the song?"