A mechanic in the 1996 Nintendo 64 game, Super Mario 64. Because of how the game processes
Mario's position, it is possible to be really
far from the actual level while still able to interact with the floors and walls, as if another copy of the floors and walls were there, hence the name "parallel universe". It was made popular by TASer pannenkoek2012 in his
YouTube video "SM64 - Watch for Rolling Rocks - 0.5x A Presses (Commentated)", in which he abused this mechanic to obtain a star while keeping the jump button held the whole
time.