September 11 attacks: A series of coordinated terrorist attacks on September 11, 2001, where hijackers crashed planes into the World Trade Center towers in New York City and the Pentagon in Washington D.C., killing thousands of people.
War on Terror: Refers to the U.S. government's efforts, led by President George W. Bush, to combat terrorism worldwide following the September 11 attacks.
PATRIOT Act: Passed in response to the September 11 attacks, this law expanded surveillance powers of intelligence agencies and enhanced law enforcement capabilities in order to prevent future terrorist activities.