SIDs stands for sudden infant death syndrome. This term describes the sudden, unexplained death of an infant younger than 1 year of age. Some people call SIDS “crib death,” because many babies who die of SIDS are found in their cribs. However, cribs don’t cause SIDS. Health care providers don’t know exactly what causes SIDS, but they do know: The back sleep position is the safest, and every sleep time counts.