What does this actually mean??

It means he /she likes you! He or she is looking at you because they find you attractive.

It means they are sizing you up. For guys it could mean anything from is she a DD to how pretty are her eyes? Is that her natural hair color? How would she look in a dress instead of jeans? Is that a thong? Is she sharp or ditsy? Graceful or awkward? Is she wearing a ring? Is she alone or is there a boyfriend close by? Contacts or real eye color? Hair extensions? Wow she's that tall in just sneakers? Does she look back at me? Is some guy's name all over her organizer or tattooed on her "back"? Which car is hers? Take your pick. Anything a guy might want to know about a girl that he can find out by looking is checking you out. Maybe it comes from library terminology. If you wonder if a book or record is worth having, check it out.

Basically he/she is looking at you with intent. He/she is not just trying catch a glimpse but almost studying your behavior. He/she is trying to take in as much as possible and see if you would be a good match for him/her. It can be a simple as a glance but usually is more.

I imagine it means looking at someone from his or her feet to his or her head and deciding if he or she is "hot and/or sexy".

basically, if someone checks someone else out, they're not interested in a long-term relationship, they want action, they want a one-night-stand, kind of stuff.

Though someone might use the phrase "to check someone out" to just mean that the person is innocently looking at you, though usually if someone means that they'll just say, "That person looks interested in you".

"To check out" has negative connotations, but remember, it isn't always bad, because bad is relative. If you want someone to think you're hot and sexy, then I imagine you'd want them to "check you out".

The guy actually told you he's checking you out? That's different. I think he's just blunt, and it simply means that he's checking you out-just making sure your what he wants physically.

maybe checking you out means he's interested in you or he wants to know something about you.