A spinner is a petite woman. Denoted as a joke, whereby the woman is so small she is able to be mounted and spun in a circle on an erect penis. Related questions (More answers below)

Spinner  (Adjective  Slang) Used among some men to describe an extremely petite young woman, usually with a lot of sex appeal  the term is thought to reference the small stature and weight of the woman; (IE she is so petite she could be spun around while riding the man during sex).