What is a ziggurat?

Having given the above question as a description of my upcoming exam to those who asked, I thought that it would be asking for trouble not to swot up just a leetle bit on the ole ziggurats. Just as well, because the question did come up and, for example, the only way I could think of dividing the Egyptian gods was into small ones and large ones. Did you know that evidence points to the Hebrews being in the stone age while living among bronze age Canaanites? Didn't have time to chase that up, and that is the story of most of my academic efforts. Somewhat disappointed that all the careful swotting up (at least half an hour at some ungodly hour this morning raking through web pages) of the identity of the Hebrew bits of the deuterocanonicals found in Qumran was for nothing, but mostly relieved I got away with having completely and utterly forgotten about Egypt in revising for an OT geography/archeology exam. Completely. Utterly. Forgot. About. Egypt.