A T-shirt is a soft cotton shirt with short sleeves, no collar, no buttons, and a round opening at the neck that you pull over your head. It is called that because when you spread it flat, the body and the two sleeves make the shape of a capital T. It started in the 1920s as men's underwear — soldiers and sailors wore it under their uniforms — and only after the 1950s did people begin wearing it on its own as ordinary clothing. That history still leaves a small trace: in some formal settings a plain T-shirt can feel too casual, like being seen in your underclothes. Today it is probably the most-worn piece of clothing on earth, and it is also a surface people write and print on — band names, jokes, slogans, protest lines. 'T-shirt' is the standard spelling; 'tee shirt', 'tee', and 'teeshirt' also appear, and 'a tee' is common in shops and casual speech. A version with long sleeves is a long-sleeved T-shirt, which sounds odd but is what people say.