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 defined as
The word altitude is often used to mean the height of a triangle.

However, on it is preferred if the terms altitude and height are used specifically to mean the perpendicular and its length, to avoid confusion.

Also see
Altitudes are a type of Definition:Cevian.