From the back of the box:
Put yourself in the pilot's seat of an advanced AGX hypersonic fighter! The year is 2096 and the time is now. Your mission is to destroy COMPUTER CONTROL, a renegade CPU out to take over the universe. You'll fly in low over awe-inspiring scenery whose beauty just might be your end. Guarding the approach to its fortress is an endless array of computer controlled FLAK batteries. They always seem to know where you are and where you'll be. You fire, evade, fire again... Your hand tightens around the flight control, you push harder on the fire button, the tension builds... Can you take it? Will you survive the FLAK?
Flak is a vertically scrolling shoot-em-up. Your aircraft must try to infiltrate enemy territory to destroy the Computer Control. This is achieved by flying low and destroying the Flak (Anti-aircraft) batteries on the way.