Thanks, Gustavus, that helps a little. I mostly deal with ewaste, and am interested not so much a definition, but when it becomes hazardous. Here's what I found out so far from this EPA publication at http://www.epa.gov/osw/inforesources...ing/hwid05.pdf

Hazardous waste identification begins with an obvious point: in order for any material to be a hazardous waste, it must first be a waste. But, deciding whether an item is or is not a waste is not always easy.
That's about as close an answer as I suppose I'll ever get...