I'd generally associate the term with being twice the value of the big blind, which as MMM says, is used in limit poker games to define the biggest bet. Win rates used to be expressed as big bets per 100 hands, but expressing win rates as big blinds per 100 hands now seems standard. Big bets is expressed as capitals BB in forums, whereas big blinds are expressed in lower case bb. 5BB = 10bb.

I've heard the term "big bet games" a lot recently though when reading about high stakes action at PLO. I guess that's because PLO is technically a limit game?