Meaning of "active shooter" in news stories

I don't understand the way "active shooter" is being used in news stories relating to people being shot at an Arkansas night club.

The Guardian:

Police said the shooting at Power Ultra Lounge was the result of a dispute among club-goers and not an active shooter or terror-related incident.

Apparently the actual police statement was:

We do NOT believe this incident was an active shooter or terror related incident. It appears to have been a dispute at a concert

What is the distinction between an "active shooter" and other shooters who are intentionally shooting people?

Solution 1:

The Little Rock police were not using the phrase correctly. The Arkansas shooter was indeed active "in a confined and populated area" during the shooting therefore he was an active shooter (per USDHS definition given by other answerer).

The term is used so people (including first responders) can know whether the shooter is still active and dangerous or the threat is neutralized (for whatever reason).

See image below for an example of the correct usage:

Solution 2:

Wikipedia says that "active shooter names the perpetrator of a type of mass murder marked by rapidity, scale, randomness and suicide".

And the United States Department of Homeland Security (pdf) defines an active shooter as "an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms(s) [sic] and there is no pattern or method to their selection of victims".