Raising in poker is the action of increasing the active bet size. There can be multiple raises during one betting round, and players can raise both preflop and postflop.
For example, let’s say you are playing in a $5/$10 game, and your opponent on the button opens to $20, and you 3-bet his bet to $70 from the SB where BB decided to cold call. In this situation, both of you have made a raise while BB only decided to cold call. Button initially raised by opening the pot to $20, and you re-raised his bet to $70 by raising one more time.