# Definition:Involute

## Definition

Consider a curve $C$ embedded in a plane.

Imagine an ideal (zero thickness) cord $K$ wound round $C$.

The involute of $C$ is the locus of the end of $K$ as it is unwound from $C$.

## Historical Note

The concept of the involute of a curve in the plane was first introduced by Christiaan Huygens during his analysis of the cycloid in his $1673$ treatise Horologium Oscillatorium sive de Motu Pendularium.