Metaphysics is the branch of philosophy concerned with explaining the nature of the world. It is the study of being or reality.Geisler, Norman L. "Baker Encyclopedia of Christian Apologetics" page 446. Baker Books, 1999 It answers questions such as: What is real (see realism)? Is it natural (see naturalism) or supernatural (see miracles)?
A central branch of metaphysics is ontology, the investigation into what categories of things are in the world and what relations these things bear to one another. The metaphysician also attempts to clarify the notions by which people understand the world, including existence, objecthood, property, space, time, causality, and possibility.