ANSWER
AB is the altitude of the triangle.
EXPLANATION
The perpendicular height of a triangle is called the altitude of the triangle.
The altitude is the line segment that moves from one vertex of the triangle and meets the opposite side at an angle of 90 degrees.
It is not always the case, that the altitude of a triangle lies inside it.
Sometimes the altitude of the triangle can lie outside the triangle.
In the diagram AB is the altitude of triangle AXZ
