Overpair
A pocket pair higher than every board card. Strong, but vulnerable on coordinated boards.
Raise pocket jacks from the cutoff, the button calls, and the flop comes 9-8-4 with two spades. Your jacks are an overpair, higher than anything on the board, and probably still best. But a flush draw and straight draws are live, and someone could already hold two pair or a set. Put those same jacks on a 9-8-4 rainbow flop with no flush draw: same hand, much less trouble. The pair didn't change. The board around it decides how much of your stack belongs in the pot.
An overpair is a strong one-pair hand, ahead of top pair and every worse pair, but it is not the nuts. On a dry, disconnected board it will stack most one-pair hands, so bet it for value across three streets. On a wet board — suited, connected, or both — it is still ahead right now, but charge the draws and watch for a raise. A flush or straight can land on any later card without warning.
The common beginner mistake is playing every overpair the same regardless of texture: jamming queens on a 10-9-8 two-tone flop with the same confidence as on a 2-6-9 rainbow flop. An overpair loses to any two pair, set, straight, or flush already made. Calling down three streets on a scary board because it is still an overpair is a fast way to hand off a stack you never had to risk.