A bet that is made when re-raising a 4-bet and increasing the size of the pot is known as a 5-bet.
In this scenario, the big blind is seen as the first bet, an open raise is considered the second bet, the initial re-raise is the third bet, a raise after that is a fourth bet, and the fifth aggressive action is the 5-bet.
To put it in short, if you decide to raise over a 4-bet, that is considered a 5-bet in poker.
The term 5-bet is exclusively used in preflop situations since making 5 raises after the flop is almost impossible.While it can happen, it requires very deep stacks and a specific situation, so this term is used to describe preflop action.
For example, you are playing in a $10/$20game, and you have AA on the Button. HJ raises to $45, everyone folds, and you make a 3-bet to $120. The action is back to HJ, who 4-bets to $270. Since you are holding the best possible holding, you raise again to $575, thus making a5-bet.
A 5-bet helps you put additional pressure on your opponents by building the pot when you have it and forcing them to fold many hands if they are 4-betting too often.