There are different /kinds/ of flirting, fo' sho'.
1) Carry-On Flirting - you know, making innuendos out of anything. Nudge-nudge, wink-wink, say no more! Oo-err missus.
2) Joke-Flirting With People Who'd Knowingly Never Get It - I do this a lot as a joke with workmates (most of whom are 40+, married with children), or some older gentlemen (like really old, 60/70+) because it gives them a nice little twinkle in their eye..!
3) Feminine-Wiles Flirting - come on guys, if you could bat your eyelashes and lean a bit further forward at a bar to get served faster - you would.
4) Flirting With Intent - because you really fancy someone, want them to flirt back, want to be suggestive and hopefully engage in some other, closer activity. This is the one that's cheating. Also known as 'leading someone on'.