The pose is very sexually provocative and is often assumed naturally by women during intercourse or as a visual prompt to initiate sex.
The term is derived from 'akimbo' - a similar posture involving the arms - the hands are placed on ones hips with elbows bent and pointing outward, thus forming the same diamond shape.
Derived from akimbo: A similar posture of the arms in which the hands are placed on the hips and the bent elbows point outward.
May also be used as a general term of a loose woman.
Campbell? Yes, she's always got her legs akimbo...