On Friday, The Fix's Chris Cillizza put to his Twitter users a question that's stirred some significant debate over the past few days: What should we mean when we use the term "mass shooting"?

The FBI defines a "mass killing" as an incident in which three or more people are killed -- a slightly broader definition than it used to use, in which the threshold was four. As The Post's Chris Ingraham noted in a recent look at the use of the term, the government doesn't define "mass shooting," leaving that evocative term subject to interpretation.

There are competing arguments about what standard should apply for a phenomenon that most would agree is worth tracking. Users of Reddit.com's anti-gun group Guns Are Cool created ShootingTracker.com, an index of news reports about shootings in which four people were injured or killed by gunfire. It's an imprecise tool, as critics readily point out, including things like incidents in which people were caught in cross-fire.

More rigorous is Mother Jones's mass shooting database, which includes only incidents in which four or more were killed. That database itself is incomplete and tends to be focused on attention-grabbing incidents, missing events like this one in November in which six people were shot to death at a campground in Texas. (One of the creators of the Mother Jones index defended their definition in a recent New York Times editorial.)

So Cillizza asked: What should count? This was not a scientific poll, by any stretch, but it was useful for the purposes of engaging people in the conversation.

The results were lopsided.

But the comments were often insightful, considering intent and context -- and revealing a comfort with ambiguity.

It's worth singling out a response that zeroed in on a particularly accurate aspect of the debate. Attitudes on what should constitute a mass shooting are often closely linked to the political views of the person considering the term. (This, after all, is why the Reddit group started collecting news stories.)

The Post's Kevin Schaul made a tool that allows you to see how many "mass shooting" incidents there have been, depending on your definition of "mass shooting." If you apply the Mother-Jones/four-killed definition to the ShootingTracker data, for example, there have been as many as 40 incidents so far in 2015.

If Cillizza's Twitter followers are any guide (please add your own jokes here) that may not be a satisfying compromise. But without an agreed-upon definition, ambiguity may be the best we can expect.

A note/update: An emailer points out that all of this discussion exists in parallel with

overall since the 1990s -- context worth noting.