What is the name of the side opposite the right angle in a right triangle?

In a right triangle, the side opposite the right angle is called the hypotenuse. This is a fundamental concept in geometry. The hypotenuse is not only the longest side of the triangle, but it also has a special relationship to the other two sides, known as the legs. According to the Pythagorean theorem, the sum of the squares of the lengths of the legs is equal to the square of the length of the hypotenuse. This relationship is crucial for solving various problems in geometry and trigonometry involving right triangles.

The other terms, such as "leg," refer specifically to the two sides that form the right angle. The "base" can sometimes refer to one of the legs when a triangle is oriented in a particular way, but it is not a general term that applies specifically to right triangles. The "altitude" is the perpendicular distance from a vertex to the line containing the opposite side, which does not describe a side of the triangle itself. Thus, hypotenuse is the most accurate and fitting term for the longest side opposite the right angle in a right triangle.