A mass shooting is defined as an event that kills four or more people involving a fire arm.
In the link that is attached below, an expert and professor from Harvard University who has studied gun violence for many, many years is interviewed on how he believes that America can reduce its gun violence. Many have the answer, we just need to produce the solution.

To the left is a chart of the deadliest mass shootings in America to this day. I believe that mass shootings can be avoided; the evidence lies in other countries that don’t even come close to the number of mass shootings we have per year. It is our jobs to be the change as this problem grows more and more deadly.