As I understand it, imaging and staging are the ability of a speaker(s) to make the sound "seem" to be coming from a location appropriate to a stage. Ex. if you're listening to classical, it should seem as though there is a full orchestra/symphony/whatever in front of you -- not right in your face, but a comfortable distance away, as though you're in the audience. This is highly subjective, though, because for some people, no matter how good the setup is, their brain will simply defeat their ears by saying, "No, you moron, the speaker is two feet away from you". With a live recording, a really, really good SQ setup, and finely tuned ears, imagining/staging will let you pinpoint where the singers are on stage, where each instrument is, etc. But really, for most folks, this is not easy to do. "Perfect" imaging is possible in theory, but it all depends on how well trained your ears are.
Tell you what, go to your local high-end home audio shop and ask to demo some Paradigm Studio 100 speakers with a CD you have (not burned with MP3s -- a real CD is best). Listen for 25-30 minutes, very closely. You'll start to notice a lot of things you probably didn't notice before. Now go listen to that same CD in your car. Unless you've got a very well built system, it's going to sound significantly less transparent than the Paradigms. But then, most of us don't spend $2000 on a pair of car speakers, either (which is what those Studio 100's cost).
I know some people will flame me for using home stereo speakers in comparison here, but I think it's a valid point.