Normal. The math word 'normal' means to be at right angles, or meeting at 90° In the figure below the line JK is normal to AB. The usual way of saying this is that JK is perpendicular to AB.
JK (or any other combination of letters) doesn't stand for anything in geometry. The purpose of these letters is to reference certain angles and sides of a figure without having to describe the angles/sides in relation to other angles/sides to know exactly which angle or side is being referenced.
