steam - representing an industrial age form of technology, steam powered generators and the like. In fantasy, this also take the form of clockwork, coal-powered artificial men, steampowered armor suits, primitive firearms and the like.
punk - an outlook on life characterized by percieving the world as an anarchic dystopia.
steampunk -- often used to represent such fantastic things as the visions of Jules Verne or H.G. Wells, but that leaves the punk completely out of it -- those are scientific romances, more strictly speaking. Mix in some Dickens for the seedy side of victorian fantasy, and you've got yer classic steampunk. IK mixes steampunk elements with a more traditional (rather than Victorian) fantasy, which is a mix I quite like, and I'm actually homebrewing something that bears no small resemblance to the Iron Kingdoms vision.