LAG is an abbreviation for “loose-aggressive,” a poker playing style marked by a high number of hands played and a lot of betting and raising. A LAG player gets involved in many pots, and when they do, they’ll put pressure on other players with big bets and unexpected raises.
When poker players use this term, you could hear them say something along the lines: Jim 3-bets every button, and he check-raises on the flop all the time; he’s a real LAG.
As far as poker playing styles go, LAG can be very tricky to play against. The biggest problem these players have is that their preflop hand selection is poor, and their bluffs don’t always make much sense. Often, they’ll bet and raise just to be aggressive and win pots by brute force.
However, a good LAG will eliminate most of these shortcomings, and will develop a solid balance. At this point, they become some of the hardest players you’ll encounter because they’ll put you to the test, whether they have a big hand or a pure bluff.