A funky and usually happy music piece, often very small, written to sound like the music found in vintage computers like the commodore 64.
A whole range of trackers like d0h, radix, rez or reflex have made memorable chiptunes. Usually chiptunes composers are specialists.
If you want to experience what chiptunes sounds like, just check the biggest chiptune archive to this date, www.chiptune.com created by rez.