quadfold
An insanely difficult contortion position in which the performer starts by laying on their stomach and bending their back until their thighs are parallel (or at least almost parallel) to the ground, effectively creating a knot out of their body. A variation of this position includes bending the knees to compress the performer even further.
Due to the tremendous amount of flexibility required to perform this position, it has never been confirmed whether it is humanly possible or if anyone has ever managed to achieve it. As of now, the performance of the quadfold remains fictional.