What act of terrorism occurred on September 11, 2001?
It was a series of coordinated aircraft-hijacking related terror attacks carried out by al-Qaeda (there were no bombs involved in any of the incidents).
On September 11, 2001 four coordinated attacks were carried out on U.S. soil at the hands of al-Qaeda an Islamic terrorist organization.
Often the first and second attack are referred to as just one attack (even though they used two planes and attacked two separate towers, it was part of one plan). These attacks targeted the two World Trade Center towers in New York City. These were, and may still remain to be, the most poignant attacks carried out by al-Qaeda. Two commercial airplanes, one for each tower, departed Boston's Logan Airport and were subsequently hijacked by al-Qaeda operatives. The hijackers then flew the planes into both towers at the World Trade Center. The ensuing destruction resulted in the deaths of 2,606 people in and around the towers along with another 147 passengers on board the planes (10 hijackers were also killed). The attack on the World Trade Center was, and still is, the most destructive terrorist attack to date (in number of fatalities and monetary cost).
The third attack carried out by al-Qaeda operatives was the hijacking of Flight 77. Flight 77 departed from Washington D.C. en route to Los Angeles, shortly after taking off 5 hijackers took control of the aircraft and deliberately flew it into the Pentagon (the headquarters of the United States Department of Defense). All 58 passengers on board perished along with 125 Pentagon officials on the ground and all 5 hijackers. There were also 106 non-fatal injuries.
The fourth attack was unsuccessful though it is believed that either the White House (where the U.S. President resides) or the Capitol Building (where the legislative houses are located) were the intended targets. Flight 93 took off from Newark International Airport en route to San Francisco. Approximately 45 minutes into the flight the plane was hijacked, the passengers became aware of the hijacking and staged a revolt which resulted in Flight 93 crashing into a field in Pennsylvania thwarting the attack on hijackers' intended target. In total 40 passengers and crew were killed along with 4 hijackers.
I remember watching the aftermath of the attacks on the morning news.
I hope this helps!