The Absolute Zone (절대영역, Jeol Dae Yeong Yeok, also known in Japanese as 絶対領域, ぜったいりょういき, Zettai Ryōiki) refers to the zone of exposed skin between the top of a girl's knee socks and the bottom edge of her mini-skirt. The perfect skirt's length to absolute zone to socks height ratio is sometimes cited as being 2.5:1:4 with a tolerance of ±25％ although preferences do vary.
Fig 1: Absolute Zone on a girl with a maid uniform
Although of Japanese origin, where the term is popular among Otakus and perverts of all sorts, the word has enjoyed an increased popularity on Korean bulletin boards over the past few years. Preferences vary between the two countries, with Koreans often showing a preference for a little "chub" as explained in the following comic. The author explains that while skinnly legs are perfectly fine, his personal preference tends to go towards legs where the flesh is slightly "overflowing".
오버니삭스 (o beo ni sak su: over knee socks): knee socks
노출하다: expose/flash (cleavage or skin)
허벅지: the inner part of a thigh