Which is why I have to agree with Gank on this, the acronym NBC is much better suited to describe these weapons as a class. WMD implies magnitude, but that's not how it's being used. In fact WMD for chemical and biological weapons is somewhat of a misnomer, neither one actually destroys anything other than living tissue (and some localized burning, in the case of strong chemical agents, but that's irrelivant to this discussion). The point is, a small amount could in theory kill a lot of people, and cannot be detected as easily as conventional explosives can.
I, for one, have gotten quite sick of "Teh terrorists are coming with ther weapons of mass destruction!!!111oneone" routine, but it's all the general public seems to be able to understand. Education is an invaluable thing, more people should really try it.