The term set is commonly used in community card poker games to refer to a three-of-a-kind hand made from two hole cards (pocket pair) and one community card.
For example, if you have a pair of nines in your hand and the flop comes K 9 3 producing another number nine card, you would say that you “flopped a set.” This term is different from trips, which also refers to three-of-a-kind, but in that case, it is made with one of your hole cards and two community cards.