Coccyx

The coccyx (Latin: os coccygis), commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five (usually four) fused vertebrae (the coccygeal vertebrae), below the sacrum. It is attached to the sacrum in a fibrocartilaginous joint, which permits limited movement between them.

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The coccyx is regarded as vestigial in humans, meaning it no longer serves major functions it did in ancestor species of humans. (Those included supporting a tail and accommodating its nerves.) It does provide an attachment for muscles, such as the gluteus maximus, and also serves as something of a shock absorber when the person sits down, although forceful impact can cause damage and subsequent bodily pains.

Vertebral column: The vertebral column (backbone or spine) is a column of vertebrae situated in the dorsal aspect of the abdomen....

Vertebra: Vertebrae (singular: vertebra) are the individual bones that make up the vertebral column (aka spine) — a flexuous and flexible column....

Sacrum: The sacrum (os sacrum) is a large, triangular bone at the base of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part or base articulates with the last lumbar vertebra, its apex with the coccyx. It is ...