In a right triangle, the cathetus (plural, catheti) is either one of the two sides which, in a right triangle, are adjacent to the right angle. The remaining side, opposite the right angle, is called the hypotenuse. The cathetus is far more frequently known as a "leg" of the right triangle or, by the periphrasis "side about the right angle". When they are related to the hypotenuse, the catheti are often referred to simply as "the other two sides".
If a right triangle is not isosceles (i.e. it is scalene), then its catheti have different lengths and a distinction can be made between the "minor" one and the "major" one.
In Euclidean geometry, the lengths of the catheti are related to the length of the hypotenuse by the Pythagorean theorem.
