Targeting control was a function of a starship's tactical control systems, specifically, it was "means" of firing weapons, such as phasers.
Prior to the initial engagement with the Dominion in 2370, Lieutenant Jadzia Dax and Odo flew aboard the USS Mekong. As the Jem'Hadar fighters were detected coming into range, Dax instructed Odo to man the helm, while she handled the targeting controls. Later, during the battle, the Mekong was hit causing Dax' control panel to go dead, as the runabout simultaneously lost sensors, forcing them to break off and initiate evasive maneuvers. (DS9: "The Jem'Hadar")
In 2374, the USS Voyager was raided by a number of ships operated by Tau that possessed a translocator device which beamed away multitude of materials and components. In her attempt to stop the thiefs, Captain Kathryn Janeway instructed Lieutenant Tuvok to "fire at will", however, Tuvok responded that "I have the will, but not the means, Captain. Targeting control is down." It was further determined that the ship's main computer processor had been removed, and with that, the ship lost its weapons, navigation, and propulsion abilities. Once Voyager's backup systems came online, the ship's phasers were restored, but their operation required manual targeting. (VOY: "Concerning Flight")