A standard design name for a particular sofa–or chair–with low sides and back of the same height, distinctively rounded. The seats are sprung and may also be buttoned, as may the inside of the arms and back.
The chesterfield is self-sufficient, requiring no loose cushions, as the upholstery is deep enough and squashy enough on its own. Of course, extra cushions increase the level of comfort, but they are not an integral part of the design. Chesterfield sofas sometimes have one or two drop arms–these can be let down to make the sofa longer and into a day bed.