In the field of weaponry, terminal guidance refers to any guidance system that is primarily or solely active during the "terminal phase", just before the weapon impacts its target. The term is generally used in reference to missile guidance systems, and specifically to missiles that use more than one guidance system through the missile's flight.
Common examples include long-range air-to-air missiles that use semi-active radar homing (SARH) during most of the missile's flight, and then use an infrared seeker or active radar homing once they approach their target. Similar examples include surface-to-air missiles, anti-ballistic missiles, and some anti-tank missiles.