1. It means a girl, guy, or
pervert is checking you out.
2. Someone meant to do :) instead of ;) and it was simply a
typo.
3. Someone is sharing an inside joke.
4. Someone is just winking at you except it's in text and nothing more than that.
1. Hey girl, wanna go out tonight? ;)
2. I got an A on my science test! ;)
3. Remember that time when Jake got fruit punch in his dick? ;)
4. Whatever, dude ;)