絶対{ぜったい}領域{りょういき} is a slang term that refers to the visible bare skin from the bottom of a woman's skirt to the top of her thigh high stockings. Or, short pants and thigh high boots... pick your preferred style. The point is that it's the exposed part of the thigh.
That's the meaning, but where did it come from?
Directly translated, it means "absolute territory". The territory part I get - it's an area on the body. But "absolute"? I find that hard to parse. Other meanings for 絶対{ぜったい} are "unconditional" or "unmistakable", but regardless of the translation choice, I find them all odd choices. Why 絶対{ぜったい}?
"Absolutely" sexy or "unmistakably" sexy perhaps?
Lastly, is this term regulated to otaku types who are into anime, or is it in common use?
