What does is mean when a guy winks at you?

I was being teased by two guys in my class at college the other day, I rolled my eyes at them and looked away, and caught the eye of another guy in my class. He smiled and winked at me, then said something to his friend. What does the wink mean?
By the way, I don’t fancy this guy, so no answers saying “wink back if you like him” etc.
Also, can I have serious answers, please? No stupid comments. Thanks :)
Yes, I’m a girl.