Guerrilla warfare is a form of unconventional warfare in which small groups of irregular military, such as rebels, partisans, paramilitary personnel or armed civilians, including recruited children, use ambushes, sabotage, terrorism, raids, petty warfare or hit-and-run tactics in a rebellion, in a violent conflict, in a war or in a civil war to fight against regular military, police or rival insurgent forces. Although the term "guerrilla warfare" was coined in the context of the Peninsular War in the 19th century, the tactical methods of guerrilla warfare have long been in use.
https://en.wikipedia.org/wiki/Guerrilla_warfare