Abbreviation for Loose Aggressive Poker Player. It is mostly used in the online poker world. A loose aggressive player is willing to play with a high risk playing style by coming out betting and raising to place other poker players under pressure in the hopes of getting them to fold. If you have this type of player at your table, you can never be sure if he has a good or bad hand.
Playing against LAGs: Just wait until you have strong hand and let him fall into the trap. The aggressive player will bet large sums to kick you out of the game. So next time just wait until you hit the flop hard and then call his bet only. Next, on the turn he will then either check or what usually happens, put a large bet in the pot to force more pressure on an opponent. Depending on the board texture and whether or not you think they have some type of hand, you can still either just call this bet or move all-in. In either scenario, you will stand to win a decent sized pot.