What is the name of the longest side of a right triangle?

In a right triangle, the longest side is called the hypotenuse. This side is opposite the right angle and is crucial in applications of the Pythagorean theorem, which states that the square of the length of the hypotenuse is equal to the sum of the squares of the lengths of the other two sides (the legs). The hypotenuse is always longer than either of the legs, making it a key concept in trigonometry and geometry. Understanding the relationship between the hypotenuse and the legs can also help in solving various mathematical problems involving right triangles.