Slate's Explainer has a pretty good explanation of what assault weapons are and they aren't (for instance, it turns out that they aren't fully automatic -- have I ever mentioned that?). One flaw, though, comes in the perennial attempt to explain how "assault weapons" are different from the tens of millions of other semiautomatic guns out there (other than, for instance, in having bayonet lugs):

The law's authors had to be as precise as possible in crafting the ban, since the phrase "assault weapon" isn't really part of the gun-making vocabulary. Rather, it's a catchall term that gun-control advocates define as covering any firearm designed for rapidly firing at human targets from close range.

The trouble is that nearly all handguns are designed for rapidly firing at human targets from close range. They're mostly intended for self-defense, not hunting (hence human targets). They're relatively short-range weapons, as opposed to rifles. And they're designed for rapidly firing, since if someone is attacking you, you'd like to shoot at him several times before he shoots you (or knifes you or clubs you).

If I recall correctly, about half the 80 million or so handguns in civilian hands in the U.S. are semiautomatics. To my knowledge, "assault weapons" don't fire materially faster than semiautomatic handguns; certainly rate of fire isn't part of the definition of "assault weapon." Most of the other half are revolvers, which to my knowledge have a theoretical rate of fire that's less than that of semiautomatics. But all of them can easily fire a round every second or two; and the main constraint is the time it takes to aim again, which means that practically speaking semiautomatics and revolvers have a comparable effective rate of fire.

So if the definition Slate gives is accurate, then virtually all handguns (except the few single-shot pistols that have to be reloaded after every round, and that thus aren't very effective for self-defense) would be "assault weapons" to gun control advocates. I don't know whether most gun control advocates do think so. But if they do, then that's further reason for gun rights advocates to worry about calls for banning assault weapons.