When you say 5NL or XXNL?

When you say 5NL or XXNL does that mean 5NL as max buyin is $5 or as big blind $5?

Also, BB is big blind and Bb is big bets? Big bets is X times the big blind?

Max buy-in.

Big bets is sort of undefined, AFAIK. BB or bb generally refers to the big blind.

"Big bet" is really a fixed limit poker term, and I don't think there's a standard abbreviation for it. In LHE and LOH it's referring to a bet on 4th or 5th street, where the bet size doubles compared to PF and 3rd street (which would be a small bet, so: two small bets = one big bet). This same concept also applies to Stud games, although with some variation depending on the exact game and certain circumstances.

Anyway, in limit poker it's fairly common to calculate the pot in terms of big bets to figure out whether or not a call might be profitable; basically it's (implied) pot odds, but adjusted for the nature of a limit game. I have also occasionally seen this term used in texts referring to NL/PL games, but, as dj correctly pointed out below, it's not a clearly defined term in that context and thus usually requires further explanation as to the author's intent.

That clears that up, thanks.

Poker Tracker uses twice the big blind to define a big bet for NL.

BB is usually Big Bets, and bb is big blinds. A Big Bet is the size of the minimum bet after the turn in limit Hold'em, but the term is used in any variation of the game to compare winrates without regard to limits.

Poker Tracker uses "BB" for "big bet", but in just about any other context, "BB" is usually "big blind", isn't it? (At least when I use it, that's what I mean by it. . . .)

Thanks for pointing that out . . . I actually noticed that after posting my answer here, but - as much as I like Poker Tracker - I'm actually not a big fan of using this formula in a NL context, because a bet of 2xBB in NL isn't even a standard raise PF, much less a reasonable bet on the later streets, so I really don't see what's supposed to be so "big" about a 2xBB bet in NL?!? I actually take out all the "BB/100", etc. columns in my Poker Tracker reports and instead, I like to use ROI for a plain, simple, and "equalized" gauge of any session's profitability, regardless of game type or limit.