Some accepted definitions of mass shootings:
Source Casualty Threshold (for injuries or deaths by firearm) Location of Incident Motivation of Shooter Number of U.S. Mass Shootings in 2015
Mother Jones (see Follman, Aronsen, and Pan, 2017) Three fatal injuries (excluding shooter)* Public Indiscriminate (excludes crimes of armed robbery, gang violence, or domestic violence) 7
Gun Violence Archive (undated-a) Four fatal or nonfatal injuries (excluding shooter) Any Any 332
Mass Shooting Tracker (undated) Four fatal or nonfatal injuries (including shooter) Any Any 371
Mass Shootings in America database (Stanford Geospatial Center, undated) Three fatal or nonfatal injuries (excluding shooter) Any Not identifiably related to gangs, drugs, or organized crime 65
Today and tomorrow there will be most likely mass shootings by the accepted definition in Philadelphia, Baltimore, Chicago, Los Angeles etc. committed by persons with an illegal hand gun.