Another name for a thong, a type of underwear or bikini bottom with a strip of fabric that goes between the buttocks. How do people wear butt thongs like that at the beach? It's so embarrassing!I could never wear a butt thong—it's too uncomfortable.
butt thong
and butt floss
n. a thong bathing costume. (Mildly objectionable.) You’re not going to wear that butt thong in public are you? My mother called my bathing suit “butt-floss!”