What is a chaise on a sofa?

A chaise, also known as a chaise longue (or, as it is sometimes spelled in the United States, a “chaise lounge”), is a long, upholstered sofa in the shape of a chair that can be used to prop one's legs upon. The name "chaise" refers to any long, reclining chair in modern French interior design, and the English translation is "long chair."