De-rendering, also referred to as phantoming, is a general term referring to the incorrect omission of one or more polygons in a scene. That is to say, a de-rendered surface or object is one that should be rendered, but isn't. Both objects and terrain can be de-rendered. And, in some cases, collision models can be de-rendered as well.
De-rendering should not be confused with de-syncing, which is also sometimes referred to as "phantoming". The shared term has caused confusion in the stunting community, leading to the creation of the terms "de-syncing" and "de-rendering".
When displaying a 3D scene, graphics engines try to find which polygons aren't visible to the viewer. The graphics engines ignore these polygons, making rendering faster and smoother. De-rendering is when the wrong polygons are ignored, causing polygons to be invisible when they should be visible.
De-rendering often occurs incorrectly when objects intersect each other or the map's terrain, or when the player reaches some location that would not be accessible during normal, non-stunt-oriented gameplay. A common example is the de-rendering of a Ghost Shroom; players observing Ghost Shrooms in certain locations may find that they de-render from certain positions. This is because the game mistakenly believes that the entire vehicle is obscured by the ground.
Sometimes when the player is outside of the normal level boundaries, particularly in ledging applications, they go "blind". This is when the entire level, or at least all of it in a certain direction de-renders. In ledging this can be quite crippling, and players have to either memorize exactly how everything looked and then attempt to perform the ledge blind, which is almost impossible, or use a third party program to clear their view. In most cases players use third person to clear their view.