Green’s Dictionary of Slang

(US black) of a woman, sitting so as to display underwear or genitals.

1971

(con. 1930s) D. Wells Night People 68: ‘Wide open spaces!’ That means a high-sitting woman. You all look out the window and when you look back there is the most disgusting seven or eleven you have ever seen. [Ibid.] 117 : high-sitting Sitting carelessly, legs apart.