Military term for Opposing Force during a combat simulations and war game scenarios.
EX: The opfor is approximately 300 meters from your position. Take care.
A term used by players of call of duty 4 to describe members of Al-Qaeda and other terrorist organisations and members often wearing head wear to cover their faces and carrying ak-47 assault rifles and RPGs or any person resembling an arab member of the gameplay.
Lets hope our boys are kicking the shit out of those OpFor bastards.