When you see a file named , it usually indicates one of two things:

A file is a "PCSX2 Patch" file. It is a plain text file containing hexadecimal codes that tell the emulator to modify specific memory addresses while a game is running. These modifications can achieve several things: Cheats: Infinite health, ammo, money, etc.

Instructions on if it doesn't match your ISO.

: By patching memory addresses to handle higher-definition assets and textures. Bypass Hardware Limits