It is the same as a re-raise and applies to both pre-flop and post-flop play.
EXAMPLE “Action folded around to me on the button. I was dealt Ace Ten and raised. The SB folded, but the BB decided to three-bet. Considering I didn’t have much of a hand and it was villain’s first 3-bet I folded.”
EXAMPLE “Holding Queen Nine of clubs on a K-10-5 board with two clubs, I donk bet the flop and the preflop raiser decides to raise. With so many outs to improve my hand I decided to three-bet on the flop.”