The term "unpaid labor" has a specific connotation akin to slavery or indentured servitude. The two are not comparable. Is this a legal term of art or common k

The term "unpaid labor" has a specific connotation akin to slavery or indentured servitude. The two are not comparable. Is this a legal term of art or common knowledge definition? It was unknown to me so I've tried some googling and am turning up primarily volunteer work and unpaid internships under that title. I know wikipedia isn't the greatest source, but over there "unpaid work" is a class of things including both slavery and working at a family business or coop.