Domestic terrorism refers to terrorist attacks committed by forces internal to or having their origin in a state, as opposed to terrorist attacks by forces external to the state. Examples of domestic terrorist attacks include the Oklahoma City bombing, the pipebombing during the Atlanta Olympics, and the sarin gas attack on the Tokyo subway.
Domestic terrorism is generally underestimated, especially within the United States: when a terrorist attack occurs the first reaction is to presume that it was committed by foreigners. That presumption was made for example in the case of the Oklahoma City bombing. The revelation that the attack was actually committed by Americans as opposed to foreigners was a shock to the people of the United States and served as an embarassment to the United States media.