LAG is an acronymn for loose-aggressive and describes a style of play where many hands are played (loose) and these right aggressively. A LAG style can be particularly profitable on high limits and in games with few players.
Types of LAG
Loose aggressive is a broad term that can also be applied to a particular phase of a player's game, so that a player might play LAG pre-flop but become more reserved in the post-flop game. Such a style is called loose-aggressive-passive (LAP), since the player plays many hands aggressively pre-flop but then decides he cannot maintain his aggression throughout the round.
A player who plays his hands aggressively all the time is a loose-aggressive-aggressive (LAA). The extreme of this style is the maniac, who bluffs, raises, and bets wildly in an attempt to win every pot with pure aggression.
A balanced form of LAA can be profitable, but requires opponents who will fold. It is particularly useless on the lower limits, where many players take many hands much too far. The value or edge of the LAA style arises from forcing opponents out of the pot often, which has the effect of making the pots smaller and also of increasing the take on good hands, since by virtue of his table image an LAA player will be presumed to have weaker hands.