Sleeveless means without sleeves. A sleeveless shirt or dress has openings for your arms but no fabric covering them. Think of a basketball jersey, a summer sundress, or a winter vest worn over a long-sleeved shirt.

Clothing becomes sleeveless by design: someone cuts and sews it that way from the start. A tank top is sleeveless. So is a vest. If you cut the sleeves off an old t-shirt to make it cooler for summer, you've made it sleeveless (though it might look pretty ragged unless you hem the edges).

People wear sleeveless clothes when they want to stay cool, show off their shoulders and arms, or layer their clothing. Athletes often prefer sleeveless jerseys because they allow complete freedom of arm movement. In hot weather, a sleeveless dress keeps you cooler than one with long sleeves. And in winter, a sleeveless sweater vest over a collared shirt creates a classic, layered look.

The opposite of sleeveless would be something with sleeves: short sleeves, long sleeves, or three-quarter sleeves. But when there are no sleeves at all, the garment is sleeveless.