State terrorism is a form of terrorism specifically used (officially or otherwise) by a standing government against its own people or enemies, in order to terrorize them into submission. This is distinct from state-sponsored terrorism, in that state-sponsored terrorism still depends upon non-governmental groups to carry it out, even while it is supported (usually secretly) by a state.
The concept of state terrorism was first identified by Noam Chomsky and Edward Herman in the late 1970s. It remains a very controversial idea in international relations, as the definition of terrorism usually involves it being committed by non-governmental actors. "State terrorism" is no different, then, from regular military or law enforcement activity in any repressive regime.
The term appears to be deliberately designed to exploit the overblown fear of terrorist attacks to criticize the unrelated issue of acts of war targeting civilians. While these acts are unacceptable, associating them with modern terrorism dilutes the meaning of terrorism to include too many "things we don't like." Events which had the "state terrorism" label applied include the atomic bombings of Hiroshima and Nagasaki, the Allied bombings of Dresden and the firebombing of Tokyo, Nazi bombings of London and Guernica, anti-communist CIA operations in Vietnam, the 2006 Lebanon War, as well as acts of totalitarian oppression in the Soviet Union.