What is the term for the lower, posterior parts of the pelvis?

The term for the lower, posterior parts of the pelvis is the ischium. The ischium forms the lower part of the hip bone and contributes to the structure of the pelvis. Anatomically, it can be found under the ilium and pubis and provides support when sitting. This bone also serves as an essential attachment point for muscles, ligaments, and tendons that are vital for movement and stability.

The ilium is the uppermost part of the hip bone and does not represent the lower or posterior aspect. The pubis is located at the front of the pelvis and is not part of the posterior region. The sacrum, while a key part of the pelvis, refers specifically to the triangular bone at the base of the spine and does not comprise the lower, posterior facets of the hip structure itself. Thus, ischium is the correct term to designate the lower, posterior parts of the pelvis.