Again, can he clarify what an “assault” weapon is?

Via Fox:

“These semi-automatic weapons, these assault weapon, can only kill people and in fact are threats to national security. The young man who did the killing in Aurora, Colorado with the arsenal he had. He was right near the airport, right near the runways near the airport in Denver. He could shoot down airplanes. so this is a matter of homeland security… We need to make manufacturers more accountable for their product.“