It’s the master configuration file that holds the game’s default settings (graphics, controls, network, etc.). When you delete or rename it, BO2 generates a fresh copy on next launch – great for fixing crashes or broken settings.
It sounds like you're asking about the file in Call of Duty: Black Ops 2 (PC version). defaultcfg call of duty black ops 2
If you meant something else – like a specific error message involving default.cfg , or you’re looking to – let me know. I can also explain how to safely restore it via Steam’s “Verify integrity of game files.” It’s the master configuration file that holds the