A nit is a player who:
- won't play a hand without very strong hole cards
- won't put alot of money in the pot postflop without a strong made hand.
Nits tend to be easily bluffed and pushed off hands and sometimes go broke with overpairs or TPTK because they fold so much preflop that once they get in a hand they sometimes have a hard time folding postflop even when it's obvious that they're beat.
Statistically speaking I think the borderline between Nit and TAG is a VPIP of 11 or so. Nits have smaller VPIP's, TAG's larger.
I would classify myself as a Nitty TAG with occasional spew problems or episodes of Nittiness. There are plenty of 6/5 Nits out there and I have never played that tight