A T-shirt (or tee shirt) is a shirt which is pulled on over the head to cover most of a person's torso. A T-shirt is usually buttonless, collarless, and pocketless, with a round neck and short sleeves. The sleeves of the T-shirt extend at least slightly over the shoulder but not completely over the elbow (in short-sleeve version). A shirt that is either longer or shorter than this ceases to be a T-shirt. T-shirts are typically made of cotton or polyester fibers (or a mix of the two), knitted together in a jersey stitch that gives a T-shirt its distinctive soft texture. T-shirts can be decorated with text and/or pictures, and are sometimes used to advertise (see human billboard).