Final answer:
A tuft of hair at the base of the spine on an infant is called a coccygeal teratoma, which is a rare congenital tumor. It can be a sign of a genetic disorder or birth defect and may require surgical removal.
Step-by-step explanation:
A tuft of hair at the base of the spine on an infant is called a coccygeal teratoma. This is a rare congenital tumor that originates from the coccyx, the small bone at the base of the spine. It can be a sign of a genetic disorder or a birth defect, and may require surgical removal. Coccygeal teratoma is one of the main keywords related to this question.