Anodyne Card 49 Fall Glitch
Video demonstration
A void warp is a glitch where you use the "Return to Nexus" or "Return to Entrance" menu options while Young is falling down a hole. It is useful for getting Card 49 (although the Wiggle Glitch is probably more useful).
If you fall down a hole then return to the Nexus from the menu, you will shift up as many screens as you have frames left to fall.