The term "ISO" refers to a file format that is an exact copy of a disc, including its file system. For gamers, having a game as an ISO file allows it to be played on a computer or through compatible devices, often without the need for the physical disc. The PSX ISO, therefore, is essentially a digital version of a PSX game. Gameshark 5.0, compatible with PSX ISOs, allowed gamers to load and play these digital copies directly through the device.