Words can sometimes be intimidating. A word like ‘metaphysics’ can even be impenetrable. Whenever I feel like I’ve grasp some sense of it, it still remains elusive. So I went ahead, and looked it up, and what do you know: I get nine, yes nine, definitions with a caveat that reads “There is no general agreement as to how to define metaphysics.”

1. the attempt to present a comprehensive, coherent, and consistent account (picture, view) of reality (being, the universe) as a whole. In this sense it is used interchangeably with most meanings of synoptic philosophy and cosmology.

2. the study of being as being and not of being in the form of a particular being (thing, object, entity, activity). In this sense it is synonymous with ontology and with first philosophy.

3. the study study of the most general, persistent, and pervasive characteristics of the universe: existence, change, time, cause-effect relationships, space, substance, identity, uniqueness, difference, unity, variety, sameness, and oneness.

4. the study of ultimate reality–reality as it is constituted in itself apart from the illusory appearances presented in our perceptions.

5. the study of the underlying, self-sufficient ground (principle, reason, source, cause) of the existence of all things, the nondependent and fully self-determining being upon which all things depend for their existence.

6. the study of a transcendent reality that is the cause (source) of all existence. In this sense metaphysics becomes synonymous with theology.

7. the study of anything anything that is spiritual (occult, supernatural, supranatural, immaterial) and which cannot be accounted for by the methods of explanation found in the physical sciences.

8. the study of that which by its very nature must exist and cannot be otherwise that what it is.

9. the critical examination of the underlying assumptions (presuppositions, basic beliefs) employed by our systems of knowledge in their claims about what is real. In this sense metaphysics is synonymous with important definitions of philosophy and also with epistemology.

Source: Peter A. Angeles, The Harper Collins Dictionary of Philosophy, 2nd ed.