A set is normally three of a kind in any game other than Omaha or Texas
Holdem. In those two games a set is referred to as a pocket pair with a matching card on the board. Trips is 1 card in the pocket with a pair on board. There is a big difference since a pair on board has quads as a nut hand and a full house as a near nut hand. Also a set has reasonable drawing possibilities to either of those two hands. I card trips is weaker since there are more hands that can beat you and the drawing possibilities are weaker. Someone else could be holding the same card with a higher kicker.