Definition:Altitude of Triangle

Definition
Let $\triangle ABC$ be a triangle.

Let a perpendicular be dropped from $\angle A$ to its opposite side $a$:


 * TriangleAltitude.png

The line $h_a$ so constructed is called the altitude of $\angle A$.

Also known as
The altitude of a triangle is also known as its height.

More specifically, the height of a triangle is used to mean the length of the altitude from the side which has been chosen as its base.

Also see
Altitudes are a type of Definition:Cevian.