A word originating from Orlando, FL having a somewhat dual meaning in referring to a girl who frequents the downtown club and party scene and is essentially "down" for whatever, generally in terms of wild partying, sex, drugs, and alcohol abuse. While this word intially had derogatory connotations it has in many circles become a term of endearment, much like "bitch", "nigga", or "motherfucker".
Fabiano: "Yo does that girl party?"
Corey: "Fuck yeah she's a sick downy!"
"I was up all night drunk as fuck, rolling my balls off, and blowing rails with six downies, smashing out on all of them!"
"That's not Lex's girlfriend, but she's his main downy. If you fuck with her he might still kick your ass!"