Improvised nuclear device

An Improvised nuclear device (IND) is a theoretical illicit nuclear weapon bought, stolen, or otherwise originating from a nuclear state, or a weapon fabricated by a terrorist group from illegally obtained fissile nuclear weapons material that produces a nuclear explosion. An IND could be bought, or it could be built from the components of a stolen weapon or from scratch using nuclear material (plutonium or highly enriched uranium).

Source: Wikipedia — Improvised nuclear device (CC BY-SA 4.0)