A large upholstered piece of furniture designed to seat several people. Also known as a "sofa."
The smallest type of couch, one that seats two people, is referred to as a "loveseat." A couch with a 90 degree bend in it is a "sectional couch," and as the name suggests is composed of several separate sections.
There may be some overlap between a small "loveseat" type couch and a large easy chair. When in doubt, just tag them as a couch.
Chaise longues (French for "long chair") are also called couches, commonly used as the stereotypical "psychiatrist's couch."