In a right triangle, the two legs are the sides that form the right angle.

### Historical note

In early treatises on geometry, the term *cathetus* generally referred to the height of a figure.

Towards the 10th-11th century, Pope Sylvester II (Gerbert d’Aurillac) wrote, in his treatise on geometry :

“A right trapezoid is simply referred to as “a trapezoid.” It has a base, a *coraustus*, or small base, and a *cathetus*.”