What is "racking off"

Usage examples of "racking off".

Instead,Defiant and the Klingons dodged through the sta-tion's pylons, racking off enough shots at the attack-ing fleet to keep from being obliterated right awaythemselves.

Instead, Defiant and the Klingons dodged through the station's pylons, racking off enough shots at the attacking fleet to keep from being obliterated right away themselves.