the.com/kept man

means A man who is financially supported by someone else — usually a romantic partner — in exchange for companionship, sex, or simply being decorative.

from The phrase rides on the verb 'keep' in its old sense of 'maintain, support, provide for' — the same sense in 'kept woman,' which is by far the older and more common phrase. 'Kept woman' dates back centuries, tied to mistresses financially maintained by wealthy men; 'kept man' is the later, gender-flipped echo, surfacing as women gained enough economic power to do the keeping themselves.