"FOX" is from the United States' standardized brevity code in the military. "FOX-1" means that a semi-active radar guided missile is initiated "FOX-2" Is an IR Missile initiate and "FOX-3" is an active radar guided missile launch. Check out http://www.christianfighterpilot.com/fighterpilotspeak.htm#fox for more information.
These are called out to tell comm of type of missile launched! "Fox 1" = semi-active radar missile (AIM-7 Sparrow) "Fox 2" = heat-seeking missile (AIM-9 Sidewinder) "Fox 3" = active radar missile (AIM-120 AMRAAM)