A shirt was a piece of clothing worn on the upper body, usually with sleeves, a collar, and buttons down the front. Shirts could be short-sleeved or long-sleeved, and are often tucked into trousers or a skirt.
After time traveling from 2373 to 1996 Earth, Tuvok refused to take off his shirt and risk dermal dysplasia due to thermal and ultraviolet radiation being at hazardous levels. (VOY: "Future's End")