Most encyclopedias will describe optical media, or discs, as a "flat, usually circular disc that encodes binary data in the form of pits and lands on one of its flat surfaces."
Technical stuff aside, optical discs and the ability to encode data onto them, and then read them back, is the technology that allowed video games to flourish as a medium because it allowed game developers to cram tons of code, audio, and image files onto a disc that's both inexpensive to manufacture and easy to duplicate.
With that in mind, we've put together a list of 10 things you probably didn't know about video game discs, while the future may be digital, there's still plenty of fascinating facts about your optical media to check out.