Car audio’ is a general term describing the sound system fitted inside an automobile. Similarly, the term ’stock car audio system’ refers to the sound system specified by the manufacturer when the car was built. A custom car audio installation, on the other hand, can involve anything from upgrading of the radio head-unit to a full-scale modification of the car based around its audio equipment - such as subwoofers, stereo CD changers, etc..

A head unit usually consists of a combination of a radio, tape player, or CD/DVD player. Newer head units are now emphasizing on digital music support (MP3, WMA, and AAC formats) and USB, Bluetooth, and Wi-Fi connectivity.

Most modern cars include at least a CD player/ CD recorder, and some have the option for car stereo CD changers, which hold multiple disks either in the head unit itself or in a separate unit usually located in a trunk or console. The main types of CD changers are External Cartridge, Internal Cartridge and Carousel CD changers.

The stereophonic sound, commonly called stereo, is the independent reproduction of the sound using two or more channels audio in way to create a natural impression of the heard sound from several directions, similar to that one in the natural hearing. In popular use, stereo audio of the car means generally the recording of 2 sounds on 2 channels and the reproduction of the sound using the data for more than a loudspeaker simultaneously.