Point defenses

Usually these are installed on larger vehicles such as aircraft carriers or warships. Even battle tanks can have basic anti-tank missile defenses. In fiction these also function as a defense against target-seeking mines.

Commonly these exist in form of fully automated gatling guns or weapon-grade lasers.

The real reason these exist is that the main weapons don't usually offer fast enough tracking capabilities (either because of mechanical limitations or because they're human operated) or are overkill (e.g. warship broadside barrage against an interceptor) for seeking and destroying these small targets.

Lack of point defenses is why Death Star was destroyed in Star Wars (the weapons it had were not designed to track and destroy small and fast craft like the X-Wing). For other similar examples of its lacking can be found from TV Tropes.