Barnacle-back is a term used to describe someone who is lazy or unwilling to move. There are several synonyms for this term, including sluggard, couch potato, loafer, laggard, and slouch. These words are often used to describe individuals who spend a considerable amount of time sitting or laying down without doing anything productive. Such people often lack the motivation or energy to engage in physical activities or work. While these words are considered informal or even derogatory, they can also help people to identify and modify their behavior to avoid being associated with a barnacle-back lifestyle.