To add on top of a previous bet in
poker; Often to get the most out of your
hand, scare other players, or straight out
bluff.
Player 1: "I'll bet 400."
Player 2: "I'll see your 400, and raise you another 1600"
Player 1: "...I'll
fold."
Player 1: "I'll bet 200."
Player 2: "I'll re-raise 2000."
Player 1: "You are bluffing, I re-raise you All In."
Player 2: ".....
fold."
Player 1: "Haha you
suck I had nothing!"