Crumple is a verb that means to become wrinkled or creased. Your face might crumple over time as you age, or you might crumple a piece of paper before tossing it in the trash.
Crumple comes from the Old English word crump meaning "bent, crooked," and it can describe something that has buckled or collapsed. If you're jumping up and down on a cardboard box, it'll eventually crumple under your weight and fold in on itself. Make sure you don't confuse crumple with the similar looking crumble, which means to break apart into small fragments. If you crumple something, it stays in one piece — it's just wrinkled or folded.