At its simplest, "PS2 highly compressed games ISO" refers to taking the original disc image file of a PS2 game (the ISO) and running it through a compression algorithm to reduce its file size.
: Games that crash during specific cutscenes or levels because the necessary data was deleted during the "compression" process.
Mobile PS2 emulation is now possible, but storage is even tighter. Highly compressed ISOs are a lifesaver on 64 GB or 128 GB phones.
Widely considered the "gold standard" for emulation today. It provides excellent compression ratios and is supported by most modern emulators.
: Widely considered the best format for PS2 games; it is lossless and supported by modern emulators like and AetherSX2.
chdman is a command-line tool bundled with MAME, but standalone scripts make it incredibly easy to use.
If you want to get your emulator running with these files, let me know: Which you are playing on (PC, Android, Steam Deck)? Which emulator you plan to use?