An ancillary weapon is a weapon used to supplement a primary or main weapon in the event it cannot be used or is ineffective in a certain application or situation. Examples of ancillary weapons to main weapons include a melee weapon to a ranged weapon, a sidearm to a service weapon, or a light gun to a heavy cannon.

Close-quarters combat (CQC) or close-quarters battle (CQB) is a close combat situation between multiple combatants involving ranged or melee combat. It can occur between military units, law enforcement and criminal elements, and in other similar situations. CQB is typically defined as a short duration, high intensity conflict characterized by sudden violence at close range.