A term popularized by the tumblr blog of the same name, an Eschergirl refers to any figure (typically female and typically within comics) drawn in a "sexy" pose that defies sense both in anatomy as well as narrative. Harkening back to the dizzying designs of Escher, these girls are also impossible.
Basically every picture of Psylocke ever.
Let's see...can see both boobs and full butt, one leg seems to be coming out of her crotch and the other one doesn't seem to be attached, her boobs are coming out of her collar and look like they're about to fly away, AND she's wearing a bikini in the middle of a blizzard. Yup, Eschergirl.