Head restraints (also known as headrests) are the padded extensions found at the top of a car seat’s backrest, designed to support the occupant's head and neck, especially in the event of a rear-end collision. Head restraints are not just for comfort—they're a critical safety feature. Proper adjustment can greatly reduce the chance of neck injuries, especially in rear-end crashes.
An adjustable headrest of a car. © Wikimedia.org/BrendelSignature, CC BY-SA