triangle flag

The visible portion of a female's traditional-back thong underwear that sticks out above a pair of low-cut jeans while the subject is sitting down (or on normal pants/shorts while the subject is bending over or at the gym). Not to be confused with string or "t-back" thongs (see "butt floss").

Dick: "You can see half that chick's ass over there!"

Harry: "I am saluting her triangle flag right now!"