(WTVM) - The FBI defines mass killings as murders that occur in a short time span and in which four or more people are killed.
There have been countless incidents in the past few years that can be labeled as a mass killing. One of the most known occurred in Newtown, Connecticut, where 20 children and six adults were killed.
Since last year's mass shooting in a movie theater in Aurora, Colorado there have been 23 mass killings, 14 of them since the first of this year, according to a database put together by USA TODAY.
The database took a look at shootings over the past seven years.
Here is a list of some of the most recent massacres in the U.S.
~In August, white supremacist Wade Michael Page fatally shot six people at a Sikh Temple in Wisconsin in what police called a hate crime. Page, 40, killed himself after an officer responding to the scene shot him in the stomach.
~After learning he'd been fired from his job, Andrew Engeldinger, 36, shot and killed five people at a Minneapolis sign company in September. He then killed himself.
~Two men were fatally shot in Mohawk, N.Y., and two more were shot at a car wash in Herkimer, N.Y., in March. Kurt Myers, 64, held police in a standoff overnight before they swarmed the building and killed him.
~In April, three people died when two bombs exploded near the finish line of the Boston Marathon. A police officer was killed a few days later after authorities publicized photos of two brothers considered suspects. One died in a standoff with police; the second, Dzhokhar Tsarnaev, 19, is charged with using a weapon of mass destruction.
~John Zawahri, 23, was shot dead by police in the library of Santa Monica College in June. Zawahri had killed his brother and father at home, carjacked a woman and shot at passersby before entering campus carrying an assault rifle.