Why does it have two names (Visual evoked potential/visual evoked response)?

Over time this procedure, has been called by different names. The word “evoked” is part of the name since active and controlled stimuli are used to drive the visual system. Because we care about how detail is being moved through the system the stimuli are various size checkerboards of different spatial frequencies. It is the changing patterns that drive or “evoke” the response.

Those who use the word “potential” are generally referring to the changes in the electrical firing levels in the primary visual cortex. Those who use the word “response” are simply looking at the entire pattern of the graph as the response the primary visual cortex is making secondary to the triggering of the stimuli. The two terms are essentially interchangeable.