A right-angle triangle is a triangle in which one of the angles measures 90°. Right-angled triangles have wide applications in mathematics and physics and as such, it became convenient to have specific names for their sides so that the problem statement in mathematics can be easily described.

One of the angles measures 90°. If we denote one of the remaining two angles by θ, then the third angle would be 90°- θ.

With reference to the angle θ, we have the below definitions:

The side opposite the right angle(90°) is called the hypotenuse. The hypotenuse is also the longest side in a right-angle triangle.

The side opposite to the angle θ is called perpendicular.

The side containing both the right angle and θ is called the base.