A some what vintage term used widely amongst the older men to rate woman. If a man and his buddies saw an attractive woman walk by they'd rate her from 1-40. 40 being a sheem - or thirty-eight-two. Therefore a sheem is a fine woman, top-notch, dime-piece... the dream woman, especially in the physical sense.
Daniel: Did you see Shelia? Damn!
Tom: Hells yea, shes fourty fasho - she's a sheem.