obama changed that definition....it used to be 4, but that wasn't giving the anti-gun fanatics the number of mass public shootings they needed...so obama changed the number to 3...
In January 2013, a mandate for federal investigation of mass shootings authorized by President Barack Obama lowered that baseline to three or more victims killed. Accordingly, we include attacks dating from January 2013 in which three or more victims were killed.
Here is Mother Jones’ groundbreaking database, now documenting 151 public attacks since 1982.
www.motherjones.com