Here are the definitions from two online dictionaries: online Collins Dictionary https://www.collinsdictionary.com/dictionary/english/couch-potato couch potato A couch potato is someone who spends most of their time watching television and does not exercise or have any interesting hobbies. online Oxford Learners Dictionaries https://www.oxfordlearnersdictionaries.com/definition/english/couch-potato?q=couch+potato couch potato noun ​a person who spends a lot of time sitting and watching television

Hi! it can be used in a way of saying lazy or inactive people, they sit around on the couch/sofa all day in the way a potato just sits underground. some people are very active meaning they may do lots of sports or exercise, whereas others are lazy and lay around all day.