It also makes sense to call it reflection rendering frequency, because the higher the setting, higher is the frequency of which the reflection updates. Lower is the opposite obviously, and you see it on the car model, the reflection are like in slow motion, but I think are still up-to-date with the reflected environment, it just reflects with less frequency = less faces per frame.
But looking at this change from the eyes of a new player to the game, is easier to understand the frequency that the reflection renders, than what is faces per frame.
(off = 0 faces per frame; ultra = 6)