Couch potato is a slang term for a person who spends a lot of time sitting on the couch watching TV or otherwise lazily lounging and loafing around.

Couch potato is often used in a mildly negative way to criticize a person for spending too much time doing this instead of doing more productive activities. But it can also be used in a more neutral way. For example, someone might say they like to relax by spending the weekend as a couch potato.