DIN refers to a standardized radio/stereo size for vehicles (large
enough to accept a CD). 1 DIN is the standard DIN specification. 2
DIN or double DIN refers to units that are twice as high as the
standard DIN, half DIN is half high as 1 DIN. International standard ISO 7736 defines a standard size for car
audio head units. The standard was originally established by the
German standards body Deutsches Institut fur Normung, and is
therefore commonly referred to as the "DIN car radio size". It was
adopted as an international standard in 1984.