Definition - What does Terrorism mean?
Terrorism is legally defined as the commission of any violent act that is specifically meant to create intense fear and advance a social or political agenda.
These acts include suicide bombings, conventional bombings, car bombings and mass shootings. Twenty-first century terrorism also includes the use of aircraft to destroy buildings and the use of vehicles for infliction of mass casualties in crowds.
Justipedia explains Terrorism
There are many examples of terrorism in which the perpetrators targeted the United States or U.S. interests.
The best known of these occurred on September 11, 2001, when foreign terrorists used commercial airliners to carry out their scheme. The attacks resulted in the collapse of the Twin Towers (the World Trade Center) in New York City and partial destruction of the Pentagon. Another commercial jet crashed when passengers turned on the terrorists/hijackers.
Other acts of terrorism in the United States include the bombing of a federal building in Oklahoma City by Timothy J. McVeigh in 1995, and the 1993 bombing of the World Trade Center.