A small, petite girl between the ages of 14-20, who has a cute face and a skinny body. It is often misinterpreted as "little girls", however, that is not the case. A girl can be 15 and have a developed body, or be 19 and look like she just started high school, and the yossi would still be the 19 year old.
Matt: Brooooooooo look over there, its a MAJOR yossi i cant believe shes in college!
Mike: Yeah shes pretty hot, she looks like she's 14 though.