Fox 1, 2 and 3 are codes for missiles (in sp: Fox 2 doesn't exist and Fox 3 is 'fire and forget' type of missile, with Fox 1 you need to maintain your lock on the aircraft).
That's how I'd explain it to someone who doesn't know Fox codes

@EasternPatrick thanks, and how do you know this?

Fox one
Indicates launch of a semi-active radar-guided missile
ㅤ
Fox two
Indicates launch of an infrared-guided missile
ㅤ
Fox three
Indicates launch of an active radar-guided missile
ㅤ
The more you know