Beatpoints are the little pink crystals spread throughout the levels. This achievement is for getting 2000 of them.
Pretty obvious, but some things that might not be so obvious:
- the big ones (called relics) are worth more, but are a bit harder to find
- you'll pretty much naturally get this playing through the game
- getting the same beatpoints while replaying levels counts
Seriously, if you're going for all the other achievements in the game, you'll naturally get this one.