Active shooter is a technical term, a phrase meant to quickly diagnose a threat, to imply certain protocols, to distinguish the risk from one that has already passed, or that wields a different weapon. It implies, by definition, a firearm. It holds out the possibility that the officers who respond might still alter the outcome.

It means, according to the definition the White House, the Justice Department, the FBI and Homeland Security have all agreed upon, “an individual actively engaged in killing or attempting to kill people in a confined and populated area."

Somehow, though, this clinical language — the language of military training, police drills and government handbooks — has migrated lately into how the rest of us talk. Children come home speaking of their "active shooter" practice at schools. Bureaucrats of all kinds get "active shooter" training, too. Homeland Security offers "active shooter" webinars and pocket cards for your local business or school.

Now when a gunman walks into a Planned Parenthood clinic in Colorado or a developmental disability center in California, the phrase appears in breaking headlines and texted alerts — although still often caged in quote marks — because it's now part of our collective vocabulary of violence.

That this technical phrase has become a common one is another sign of how the expectation of mass gun violence is now embedded in the world around us. Teachers and church leaders now know words that were once the domain of officers and dispatchers. Barely five years ago, the public hardly used them. Here is the frequency of "active shooter" in Google Trends online search data:

Go farther back in Google's digitized corpus of English-language books, and its use has risen dramatically since the late 1990s.

Last year, the FBI compiled a report of the 160 "active shooter" incidents in America from 2000-2013 and concluded that they have increased in frequency, a trend that "reinforces the need to remain vigilant" — to expand trainings and programs and education.

The more they happen, the more we talk about them, the more we need to teach children and office workers and hospitals how to think about them before they happen again.