I despise this term. To me, and millions of others, an "active shooter" is someone who participates in shooting matches often, and live-fire practices often. A person like me, who not only would not initiate force on others, but who would actively protect and defend innocents, if he could.
Not all shooters are evil, twisted murderers. When we adopt this terminology, we are playing right into the hands of the disarmist media and cultural Marxists, who want everyone disarmed.
Take it easy, this is not a slight aimed at you.
Cops need shorthand to describe a situation, so they know best how to proceed.