torsion of a curve

Torsion of a curve in differential geometry.

Quantitatively, this is measured by the differential-geometric invariants called the curvature and the torsion of a curve.

In the elementary differential geometry of curves in three dimensions, the torsion of a curve measures how sharply it is twisting.

The torsion of a curve, as it appears in the Frenet-Serret formulas, for instance, quantifies the twist of a curve about its tangent vector as the curve evolves (or rather the rotation of the Frenet-Serret frame about the tangent vector.)