What does it mean to be "fly"?

Answer 1

Cool. Hip. With it. Happening.

Answer 2

You are cool, together, hip, slick, all of these fad words, and they all pretty much mean good things about how you look, how you are dressed, act, etc.
"Oh you look fly"; "oh you fly baby", etc, or "it's fly" (ok).
However I like;
Excellent! The Brits use that a lot, when something is good, right etc Like as in Oh, excellent! when something good is offered up, or something turns out well, you know, add your own new words, it's all the same, different times is all, Remember a word "Groovy?" how corney, but people said it.

Answer 3

To be fine, sexy, cute, good-looking, whatever you wanna call it!! It just means to be hottt!