Sacrum means: Sacrum is the large, heavy bone located at the base the spine.
they are made of fused sacral vertebrae. You will find the sacrum in
The vertebral column is located between the lumbar vertebrae, and the coccyx. It
It is approximately triangular in form and forms the back wall.
pelvis. Female sacrums are wider and more curved than male sacrums.
(in Medical Dictionary)

What else does Sacrum mean?

Its Latin name is “os Sacrum”, which means holy bone. It is not clear why it was considered sacred.
(in Medical Dictionary)

Triangular bone that is composed of five fused vertebrae. It forms the posterior part of the pelvis.
(in Merlin Dictionary)