Guerrilla warfare is a form of irregular warfare and refers to conflicts in which a small group of combatants including, but not limited to, armed civilians (or "irregulars") use military tactics, such as ambushes, sabotage, raids, the element of surprise, and extraordinary mobility to harass a larger and less-mobile traditional army, or strike a vulnerable target, and withdraw almost immediately.
The term means "little war" in Spanish, and the word, guerrilla, has been used to describe the concept since the 18th century, and perhaps earlier.
The term guerrilla was used within the English language as early as 1809. The word was used to describe the fighters, and their tactics (e.g."the town was taken by the guerrillas"). However, in most languages guerrilla still denotes the specific style of warfare. The use of the diminutive evokes the differences in number, scale, and scope between the guerrilla army and the formal, professional army of the state.