What does the direction cosine of the normal vector of a plane equation mean?

What does the direction cosine of the normal vector of a plane equation mean?

The directional cosine is the cosine of the angle between a vector and the X, y and Z axes (if it is a plane, it is the cosine of the angle between the vector and the X, y and Z axes). It has one property: the sum of squares of all directional cosines is equal to 1. The directional cosine of the normal vector of the plane equation is the cosine of the angle between the normal vector of the plane equation and the X, y and Z axes, which has three properties