Impi is a Nguni word meaning war or combat and by association any body of men gathered for war, for example impi ya masosha is a term denoting an army. Impi were formed from regiments (amabutho) from amakhanda (large militarised homesteads). In English impi is often used to refer to a Zulu regiment, which is called an ibutho in Zulu or the army.

Its beginnings lie far back in historic local warfare customs, when groups of armed men called impi battled. They were systematised radically by the Zulu king Shaka, who was then only the exiled illegitimate son of king Senzangakhona kaJama, but already showing much prowess as a general in the army (impi) of Mthethwa king Dingiswayo in the Ndwandwe–Zulu War of 1817–1819.