“Fly” is how a man digs a woman. One would never describe oneself as “fly,” even when cataloguing one’s own attractions (done more in rap than anyplace except perhaps Village Voice personals). “Fresh” means irresistibly stylish, oft-modified by “funky,” “crazy,” or “stoopid,” predominantly used to convey the fly-ness of things other than women, including oneself or one’s rap, which two concepts rappers, like schizophrenics, can’t always keep separate in their heads. “Dope” means “def,” and “def” means crazy funky stoopid fresh. Synonyms include: the shit, the It, the cool, the thang, the word, the grooviest, the categorical imperative, die weltanschung, the that-which-Potter-Stewart-would-know-if-he-saw. A def rapper is so style-defining as to make the stylish mere copycats. To be def is to rap to the beat of a different drum machine–not seeking solitude, but rather confident that others will follow.
— Mark Costello and David Foster Wallace (Via)