how to use the function, ReflectionVectorWS

Hello guys,

who can help me to explain how to use the function, ReflectionVectorWS. Although I have make several tests in the material editor and observed change of the material ball, but till now, I don;t undertand about it.

In addition, the docs tell "The ReflectionVectorWS expression is similar in spirit to CameraVectorWS , but it outputs a three-channel vector value representing the camera direction reflected across the surface normal. ".

So ," the camera direction reflected across the surface normal.", what means ?