Zettai Ryouiki (絶対領域) is a term used in anime series for the area of exposed thigh when a girl is wearing a miniskirt and thigh high socks. It literally means "Absolute Territory" in Japanese.
The term comes from the anime series Neon Genesis Evangelion. To be exact, the term originated from the Absolute Terror Field (AT Field), a sort of energy barrier that makes Angels (main antagonists of the series) impervious to common physical attacks. It also denotes the barrier of people's souls.
As a Moe AttributeEdit
The presence of the zettai ryouiki, however, does not exclude non-tsundere characters. Also, it is a moe attribute, alongside megane, nekomimi, and tsundere mentioned above.