DIN refers to a German standards organization so there are lots of DIN things. Apparently, the fotmat for in-dash radios and the size of the old standard size radio is known as "single DIN". More recently, larger radios grew screens to deal with nav, camera output, etc. They are basically twice as tall, but the same width of the older radios and those are "double-DIN."
I have the music from just about every CD in my house on a micro SD card that is plugged into radio in my Mercedes. I would love to be able to do the same thing with my Lotus but the radio in it only supports a USB thumb drive. Much better, IMHO, than CDs but not as good as micro SD card but then to each his own.