An automatic firearm continuously fires rounds as long as the trigger is pressed or held and there is ammunition in the magazine/chamber. In contrast, a semi-automatic firearm fires one round with each individual trigger-pull.

Although both "semi automatic" and "fully automatic" firearms are "automatic" in the technical sense that the firearm automatically cycles between rounds with each trigger pull, the terms "automatic weapon" and "automatic firearm" are conventionally reserved by firearm enthusiasts to describe fully automatic firearms. Use of this convention can avoid confusion. Firearms are further defined by the type of firearm action used.