IMHO, a “chiptune” is music for an FM synthesis chip, like on the NES, the SID chip in Commodore 64, or the AdLib sound card for PC. A “mod” or “tracker music” is music made for a range of platforms in a rather narrow time-band, that could play digital samples, but could not reasonably store entire songs recorded digitally, like the Amiga, Atari ST, or early PC’s like 386s or 486s.