The term is more than just a file name; it represents a practical solution to a classic problem. Standard PSP ISOs (disc images) can range from 800MB to 1.8GB. However, the average PSP Memory Stick Duo (or microSD adapter) was limited to 2GB, 4GB, or 8GB.
Interesting Parallels between SSX 3 and SSX On Tour for the PSP Ssx Tricky Psp Iso Highly Compressed