teppeki skirt 鉄壁スカート

In the Japanese anime fandom, teppeki skirt, also romanized teppeki sukaato 鉄壁スカート, literally "iron-wall skirt," or less literally "impregnable skirt," refers to a skirt that doesn't let panties be seen, doesn't let panchira happen, by folding in ways inexplicable by current science and going as far as to ignore gravity and other laws of physics to cover the panties hidden within.

Anime: Mondaiji-tachi ga Isekai kara Kuru Sou Desu yo? 問題児たちが異世界から来るそうですよ? (Episode 8)

• A spell has been cast to the skirt of Kuro Usagi 黒ウサギ, "Black Rabbit," to turn it into a teppeki skirt, so you never get to see the panties she's wearing in the anime, no matter the camera angle or position of her body.
• I'm serious. It's canon. The canonical comment on it:
• mieteshimaeba tada no gehin na shitagi-tachi mo, mienakereba geijutsu da
  見えてしまえばただの下品な下着たちも、見えなければ芸術だ。
  Even panties, which are vulgar if you end up seeing them, become art if you don't see them!
  • The very essence of chiralism.