A contortionist is a performer who twists their body into strange, tight shapes to entertain people — folding in half, putting their legs behind their head, squeezing into a tiny box. You see them in circus shows and variety acts. The skill is trained; it is not the same as being “just flexible”. The word is almost only used for this kind of performer, though people sometimes joke that someone squeezing into a crowded car is “a bit of a contortionist”.