Zettai Ryouiki: The Absolute Zone
This week’s key word in the erotic Japanese dictionary is zettai ryouiki (絶対領域) — often translated as “the absolute zone”.
A major part of otaku and moe culture, zettai ryouiki refers to the area between of the upper thigh when it is being exposed by a nubile and sexy girl, particularly when she is wearing a skirt and knee socks.
The phrase also occurs in Evangelion and so possibly became slang from there.
It’s not just about the exposure of naked flesh on the leg. The amount and proportion of sock and skirt is also very important in framing and emphasizing the nudity.