posing strap
noun1
A thong-style undergarment worn by male bodybuilders or models for physique magazines.
- […] Lou was a respectful reader of the boy books that were emerging then, those magazines of black-and-white photos of teenagers with shaved chests, sucked-in if unexercised stomachs, and cloth posing-straps who stood on a dais silhouetted against a sunburst of seamless paper.1988, Edmund White, chapter 5, in The Beautiful Room is Empty, New York: Vintage International, published 1994: