T-shirts are clothes that cover the torso of the human body and the upper parts of the arms. Like underwear, they are worn in direct contact with the skin, but they are used as outer clothing.
Similar as T-shirts, polo shirts are made from knitted fabrics. They differ from T-shirts, however, in that they have a collar and a placket which is closed by buttons. Some polos have a zipper instead of buttons.
Polo shirts may be unicolored, dyed in different colors, or printed with a logo, a message or an image.