What does "lag" mean?

Answer 1

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.

Answer 2

Also in online games, including poker, lag is the delay between an action being initiated and the action having an affect on the game. So if you hit the button to fold but your position doesnt fold for 2 seconds then you have experienced 2 seconds of "lag".