When attacking a ship inside your firing arc, if you are not inside that ship's firing arc, reduce its agility value by 1 (to a minimum of 0).
A turret is not a firing arc. A ship with a turret weapon (including a ship with a 360° primary turret) is affected by Outmaneuver unless it is defending against a ship that is inside the printed, shaded firing arc on their ship token, and only gains the benefit of Outmaneuver when attacking a ship inside the printed, shaded firing arc on its ship token.
All firing arcs (including special, auxiliary, mobile, and primary firing arcs) are included for this ability. (X-Wing FAQ, Version 4.4.1, Updated 01/22/2018)