Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
It is the pelvic brim, which is the edge of the pelvic inlet. The pelvic inlet is typically used to divide the abdominopelvic cavity into an abdominal (above the inlet) and a pelvic cavity (below the inlet). Sometimes, the pelvis cavity is considered to extend above the pelvic inlet, and in this case the pelvic inlet is used to divide the pelvic cavity into a false (above the inlet) and a true pelvis (below the inlet).
Additional images
Diameters of superior aperture of lesser pelvis—female
Female pelvis
References
Kirschner, Celeste G. (2005). Netter's Atlas Of Human Anatomy For CPT Coding. Chicago: American medical association. p. 274. ISBN1-57947-669-4.
Pelvis, with dotted line marking linea terminalis
Diameters of superior aperture of lesser pelvis—female
Female pelvis
