In a right triangle, the hypotenuse is the longest side, an "opposite" side is the one across from a given angle, and an "adjacent" side is next to a given angle.
We use special words to describe the sides of right triangles.
The hypotenuse of a right triangle is always the side opposite the right angle. It is the longest side in a right triangle.
The other two sides are called the opposite and adjacent sides. These sides are labeled in relation to an angle.
The opposite side is across from a given angle.
The adjacent side is the non-hypotenuse side that is next to a given angle.
Putting it all together from the perspective of angle, A:
And from angle, B:

Practice

Problem 1
Relative to angle G, which side is the adjacent side?
Please choose from one of the following options.

Why are these words important?

We're about to learn the trigonometric functions—sine, cosine, and tangent—which are defined using the words hypotenuse, opposite, and adjacent.