The term 'Corset Bone' is a colloquial name for the 'STAY' bone, which is a four-letter word. The STAY bone is a small, flat bone located in the lower back of humans and other primates. It is part of the sacrum, which is a triangular bone at the base of the spine. The STAY bone helps to support the weight of the upper body and provides stability when standing or sitting. It also helps to protect the spinal cord from injury.