What is 'terrorism'? Boston bombings renew efforts to define pain, motives in a single word

  • FILE - In this Wednesday, April 19, 1995 file photo, an unidentified man, his face covered with blood, looks at the bombed Alfred Murrah Federal Building in Oklahoma City. Timothy McVeigh detonated explosives packed into a yellow Ryder rental truck, killing 168 people in and near the federal building. (AP Photo/David Longstreath)The Associated Press

  • FILE - In this Tuesday, Sept. 11, 2001 file photo, two women embrace each other as they watch the World Trade Center burn following a terrorist attack on the twin skyscrapers in New York. (AP Photo/Ernesto Mora) MANDATORY CREDITThe Associated Press

  • FILE - In this Friday, Sept. 14, 2012 file photo, Libyan military guards check one of the U.S. Consulate's burnt out buildings during a visit by Libyan President Mohammed el-Megarif, not shown, to the U.S. consulate in Benghazi, Libya to express sympathy for the death of the American ambassador, Chris Stevens and his colleagues in the deadly Sept. 11, 2012 attack on the consulate. (AP Photo/Mohammad Hannon, File)The Associated Press

  • FILE - In this Thursday, Nov. 5, 2009 file photo, Spc. Ryan Howard of Niles, Mich., right and Spc. David Straub of Ardmore, Okla. wait for news of fellow soldiers while waiting at the gate of the Army base after a shooting at Fort Hood, Texas. (AP Photo/LM Otero)The Associated Press

The definition of terrorism is being discussed again as the United States waits for a motive in the Boston Marathon bombing.

Experts — and the dictionary — define terrorism as the use of violence and fear to pursue political goals. There's no word yet about any motivation for the explosions Monday that killed three people and maimed scores more.

President Barack Obama didn't use the word when he spoke hours after the attack. By Tuesday, he called it an "act of terror" any time bombs are used to target innocent civilians.

That definition works for people like Jay Winuk (WIN'-uk), who lost a brother on 9/11. Others are holding back, like some history students at Kent Place School in New Jersey. They want more information before deciding what to call the Boston tragedy.