a heather is a person that you like but hate yet at the same time. she/he is so perfect and everyone likes them, they're good at everything they do, they're smart, they're funny, and last but not least, they're beautiful/handsome. maybe they're not popular, maybe they are. they know how to fix a wrong into a right, and they know sometimes things can't be fixed no matter how hard they try. and if someone calls you one, take it as a compliment!
Jason: dude that new girl is such a Heather!
Ace: I know dude, she totally is! can you believe she's Miguel's girlfriend?!
Jason: she is?
Ace: Yep!