A "head unit" is the central component of a car's audio system, typically located in the dashboard. It controls various functions such as radio, music playback, and navigation. Head units can connect to smartphones and other devices, allowing users to play music, make calls, and access apps through features like Bluetooth and Apple CarPlay. Modern head units often come with touchscreens and customizable interfaces, enhancing user experience. They may also support USB connections and SD cards for additional media options. Upgrading a head unit can significantly improve sound quality and provide more entertainment features in a vehicle.