A lagger is someone who has a horrid internet connection and lags (slows) up a
game and creates problems and annoyances for the other gamers.
Sometimes laggers
lag on purpose to create an unfair advantage over their opponents. There are methods and ways to lag a
game so that
people can't see what they're doing - yet the lagger can still play normal. This is considered cheating and if caught, the players will be banned or suspended from playing.
Lagging, whether it be on purpose or just because you're poor, is frowned upon in the gaming world.