A wince is a facial or bodily expression of pain, disgust, or regret. Think of something you've done that was really, really embarrassing or dumb: now feel your face or take a look in the mirror as you wince at the uncomfortable memory.
A moment of pain or a recollection of something painful can make you wince. It's hard not to have a physical response or a wince with a bad memory or a hurt. And wince is both a verb and a noun, so it can be an action or a result. Sometimes people don’t do anything or have any physical pain, but they wince in discomfort at what someone else does or says, as when no one laughs after a really inappropriate joke.