(covers information from several alternate timelines)
A targeting scanner (or target acquisition) was a part of transporter systems. It was used to locate objects which needed to be transported.
Targeting scanners could also be used to aim weapons at a target during a tactical scenario.
In an alternate version of 1944, Armory Officer Reed attempted to use the targeting scanners aboard the NX-class starship Enterprise to destroy a facility belonging to Vosk, the leader of the Na'kuhl. He was unable to lock on to the building with targeting scanners, so he used visual scanners instead. (ENT: "Storm Front, Part II")