Noun
The alignment of a microwave or radar antenna using purely optical means
The alignment of the bore of a gun and its gunsight in parallel
Source: en.wiktionary.org2nd Armored Cavalry Regiment soldier, assisting in the critical job of "boresighting" the alignment of all the tank's sights to the center of the axis of the bore of the main gun on an M1A1 Abrams in Mosul, Iraq in January 2005. Source: Internet
Hand signals enable the gunner (inside the tank) to train the main gun onto a boresighting target. Source: Internet