It is the same as a re-re-raise and generally applies to pre-flop play in no-limit texas hold’em games. So if a player three-bet and another player raised again, this bet would be considered a four-bet.
The concept refers to all four-betting situations, whether four-betting for value or as a bluff. When four-betting as a bluff it’s referred to as light 4-betting.
EXAMPLE “Action folded to the CO who raises. The player on the BTN 3-bets and I 4-bet small with AA in the big blind hoping to get more action out of the very aggressive BTN 3-bettor.”
The reasons for four-betting with a big hand are pretty self explanatory. If you have a premium hand like AA, KK, QQ, you want to start building the pot preflop.
Watch the video below to better understand how to 4bet light.