PU stands for parallel universe. basically you can click play then quickly click skip intro if you make a choice before the intro starts, it goes on as normal. you're basically doing 2 endings at once. I believe the WR for Stealing the Diamond Finish Endings and Fleeing the Complex Finish Endings shows this better than I can explain it.
maybe the wr holder could elaborate the wr holder currently is ElectroPindsvinet
PU glitch or Parallel Universe glitch is an exploit that allows us to play two paths/options at once. It is mainly performed by pressing Play on the menu screen and then quickly pressing Skip Intro during the "Play" animation.
This glitch allows you to, as mentioned above, play through two options at once but also opens up another exploit called Map Boosting (I think IDK what they wanna call it) which SPEEDS up an animation playing in the "background" (this can be seen in the current Any% PU WR).
you couldve just started a new thread but anyways jkr has a guide for every option in every ending in guides