A military generally refers to a permanent, professional force of soldiers or guerrillas trained exclusively for the purpose of warfare. These military forces should be distinguished from a sanctioned militia or a levy, which are temporary forces of citizen soldiers with less training who are "called up" in wartime. A military can utilize conscription (the draft) or be made up of volunteers.

Military forces have changed from the sword and spear-wielding footsoldiers of antiquity to Middle Ages soldiers mounted on horseback, to Napoleonic-era soldiers armed with gunpowder muskets and cannons. Since World War I, military forces have used motorized vehicles and rapid-fire firearms.

The term military is derived from Middle French term militaire, which is derived from the Latin word militaris, which means "of soldiers or war." The Latin word is derived from from miles, which means soldier. The term military is often used to mean an army.