A few more words on metaphysics: Metaphysics received its first formulation with Aristotle, one positioning it with respect to physics. Unless metaphysics is to be relegated in its entirety to the history of philosophy, an answer to the question, What is metaphysics?, must be contemporary.

A lot of what contributes to the difficulty of answering the question is historically contingent: the branching off of much of science from philosophy. What remains in the province of metaphysics is controversial, and much of that controversy is the product of differing views about what physics is, what it does, how it does it, and how that all differs from the methods and goals of metaphysics.

What are some of these differences? Probably the most striking difference is one of language, which in the case of physics is mathematics. If there is a clear line that can be drawn between modern physics and metaphysics, that line is drawn with mathematics. And something very interesting happens when, for purposes of general debate or popularization, scientists translate the "meaning" of the mathematics of physics into a natural language: the line dividing physics and metaphysics immediately begins to blur. The translation from mathematical equation to natural-language description will always delineate a pathway from physics to metaphysics.

This should tell us something about the two disciplines. For one, it suggests that Whitehead was right in thinking that mathematics does not constitute a model that is generalizable. The kind of necessity proper to mathematical demonstrations cannot be transferred to philosophy. For another, it suggests that there is an activity that is distinctively proper to metaphysics, and the tool for that activity is natural (as opposed to formal) language.

There is a lot of confusion (one might say 'cross-pollination') between metaphysics as a sub-discipline within philosophy, and metaphysics as a publishing-industry catch-all for squishier occult interests. This is probably due in part to the attempts by people active in the occult to acquire status by association with "philosophy." Which is not unlike many attempts by philosophers to improve their public image through association with "science." I don't know of any easy way through this confusion. But if someone is genuinely interested in gaining a clearer understanding of what metaphysics is, in its more orthodox philosophical sense, then I think Moore's book would be helpful, though admittedly it is not a casual read. If someone "really doesn't know what metaphysics is," then they are in the enviable position of having a chance at being lucky at the outset; of starting somewhere near the center of mainstream philosophy, rather than somewhere out on the dubious fringes.

Not surprisingly, your question has elicited a variety of responses, most of which, it seems to me, are just a bit off the mark. Personally, I'm comfortable with A. W. Moore's take on it, from his book, The Evolution of Modern Metaphysics: "Metaphysics is the most general attempt to make sense of things."