18.3.39 Vector3D - normalized?

Now reads: " If this value represents a normal, then it should be normalized."

normal in our 3D attributes says: "only the front sides of planes are displayed."

Ignoring that we use "normal" to mean several other things, I don't know what it means here?

Clearly the language implies some operation on the x,y,z coordinates but it isn't clear what that operation would be.