The ratio of Biddys to Dunnys (guys to chicks) at a place at a perticular time.
4 guys and 4 girls is a b-d ration of 1.0
4 guys and 2 girls is a bad bd-ratio, and is a .5
6 girls and 2 guys is a great bd ratio, at 3.0.
"Man, this 2.0 ratio is awsome, gurranteed 3 ways for every dude!)