That’s a good question — and perhaps one that should have been answered before New York jumped headlong into a ban on them.  The New York Times can’t quite figure out what the definition is, calling it “complicated”:

Advocates of an assault weapons ban argue that the designation should apply to firearms like those used in the Newtown, Conn., shootings and other recent mass killings — semiautomatic rifles with detachable magazines and “military” features like pistol grips, flash suppressors and collapsible or folding stocks.

Such firearms, they contend, were designed for the battlefield, where the goal is to rapidly kill as many enemy soldiers as possible, and they have no place in civilian life.

“When the military switched over to this assault weapon, the whole context changed,” said Tom Diaz, formerly of the Violence Policy Center, whose book about the militarization of civilian firearms, “The Last Gun,” is scheduled for publication in the spring. “The conversation became, ‘Is this the kind of gun you want in the civilian world?’ And we who advocate for regulation say, ‘No, you do not.’ ”

But Second Amendment groups — and many firearm owners — heatedly object to the use of “assault weapon” to describe guns that they say are routinely used in target shooting and hunting. The term, they argue, should be used only for firearms capable of full automatic fire, like those employed by law enforcement and the military. They prefer the term “tactical rifle” or “modern sporting rifle” for the semiautomatic civilian versions.

They argue that any attempt to ban “assault weapons” is misguided because the guns under discussion differ from many other firearms only in their styling.

Modern armies don’t design semi-automatic rifles for use in theaters of war.  They supply their soldiers with fully automatic weapons, which have been illegal for civilians to own or purchase in the US ever since the Great Depression, with only a narrow exception with strict licensing and oversight.  Semi-automatic rifles produce one round per trigger pull, regardless of how “scary” the weapon looks.  I noted the same ignorance of military use in my TFT column today with regard to how Barack Obama attempted to sell his assault-weapons ban proposal yesterday:

Let’s start with the assault-weapons ban, which mirrors the ban Connecticut had in place at the time of the massacre. Obama insisted in his speech that “Weapons designed for the theater of war have no place in a movie theater,” but the weapons banned under this proposal wouldn’t be used in any theaters of war, either.

They are all semi-automatic weapons, which require one trigger pull per shot fired, just as revolvers do.  Weapons designed for theaters of war are usually fully automatic, at least for modern armies, allowing soldiers to produce rapid continuous fire on an enemy. Fully automatic weapons are already banned for most American civilians, either for sale or possession, by existing federal law.

This was a problem with the original 1994 legislation, too.  The law banned or allowed weapons that functionally were the same.  All of them produced one round per trigger pull, but the military flourishes — which do nothing to add or subtract from the lethality of the weapon — offended the senses of some enough to warrant their illegality.  It’s strictly a superficial, stylistic choice.

The New Republic‘s Bill Scher made the same point yesterday, as well as the 1994 law’s ultimate futility:

Most glaringly, though, the focus on assault rifles ignored the main source of gun deaths: handguns. In 2011, there were approximately 6,000 homicides from handguns, versus little more than 300 from rifles. (Another 20,000 gun deaths were intentional suicides, also primarily a handgun problem.) While mass shootings are nationally traumatic, they are a mere sliver of the gun problem. The 68 dead this year from such crimes is less than one-half of one percent of the 30,000 gun deaths from 2011.

Assault weapons may be more likely in mass shootings, but so are semiautomatic handguns, which were used in Columbine, Virginia Tech and Aurora. The killers at Columbine and Aurora also used shotguns. In fact, police in Aurora noted that the shooter could have done more damage with his shotgun than with his assault rifle equipped with the infamous 100-round magazines, partly because of the deadly spray effect of the shotgun pellets and partly because his 100-round magazine jammed, as they are known to do.

Scher linked to FBI statistics on homicides in the five-year period from 2007-2011 (inclusive), and in each year — well after the expiration of the 1994 law — the number of murder victims by firearms fell from the year before.  That is true of handguns and of rifles, as well as the overall number of murder victims in the country by any means. But let’s look specifically at “rifles,” of which the assault-weapons ban would only affect a subset, and see how those stack up against other means of murder:

First, if one wants to prevent murders, then going after rifles isn’t going to do much, since murders involving rifles only accounted for only 323 of the 8,583 firearms-related murder victims in 2011, according to the FBI. More homicide victims resulted from blunt-object attacks (496), and nearly five times as many from knives and other cutting instruments (1,587).

More than twice as many victims (728) resulted from “personal weapons,” defined by the FBI as “hands, fists, feet, etc.” More to the point, the 1994 ban didn’t reduce the rate of mass shootings; its expiration didn’t increase the rate, and many of those that did occur involved weapons outside of the scope of the ban, such as shotguns and handguns. Note too that homicide victims from firearms dropped in each of the last five reported years in both overall numbers and those resulting from rifles.

In other words, we’d have arguably better results by banning human arms than from banning a subset of rifles, at least in terms of murders committed … and probably just as much success, too.  This also points out the vapidity of the term “assault weapons”: any weapon used to assault someone else is an “assault weapon.”  Handguns produced 20 times as many murder victims as all rifles, and yet all of the focus falls on styles of semi-automatic rifles designed specifically for civilian use that simply look and sound scary to contemplate.

What does this tell us?  It says that politicians hyperventilating about the style of a few semi-automatic rifles are more interested in posing than in actually addressing the issues of violence in American society.