(well first off this is the correct spelling of this word)
This term is used to describe a girl of interest who more likely then not is a little slutty or is down to fuck. (But warning some biddys are fucking teases and do not want to fuck or give head this is a term known as a bad biddy. Stay away from those!!!) There is no exact age for a biddy they can be from 14 and up. This does not mean that the girl has to be pretty, interesting, or actually fun to be around as long as she is fuckable and wants to fuck she is therefore a biddy.
-Where the fuckin' biddys at?
-Dude are you bringing your biddy to the party this weekend.
-Dude we need some bids here i haven't got my dick wet in a minute.
-Fuck man some biddys would be nice right now.