Metaphysics - what is it? Metaphysics:
Traditionally, it's:
(1) "Universal 'science'," "first philosophy" or "first principles,"--all common names for more or less core logical axioms required for things to obtain, to be coherent, etc.
(2) "Natural theology" or basically philosophy of religion
and
(3) Ontology - or philosophy of existence/philosophy of "being," nominally at "higher" levels of abstraction, but depending on one's views about the extent to which those abstractions are possible/to which they make sense, there can be a lot of overlap with the sciences here, only from a philosophical perspective/philosophical methodology rather than an approach via scientific methodology. Ontology answers questions such as "What is the world (everything extant) comprised of?" "What is its nature/ what is the nature of the components that comprise things?" "Is there more than one kind of component?" "What are properties?" "What is causality?" "What is motion?" "What are relations?" "What is time (& space/spacetime)?" etc. etc.
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It's not uncommon now for folks to think of metaphysics as more or less synonymous with (3)--ontology--only, especially if one rejects religion more or less. (1) is often thought to be best suited for logic "proper."
There's a lot of confusion due to the etymology (or rather misunderstandings of the etymology) of the name, "metaphysics." It's often taken to refer to something "beyond" physics, in the sense of transcending physics, more or less in a mystical sense. The fact that part of metaphysics is traditionally natural theology doesn't help this misunderstanding. Really, the name stems from "after" physics, and it was meant literally, in the sense of an editor who was anthologizing the work of Aristotle putting the then-unnamed book (which was dubbed "metaphysics" for the collection) after the book known as "physics." In other words, it was simply "here's the book named 'physics'" and then "here's the book after the book named 'physics.'" The content of Aristotle's book (dubbed "metaphysics") was the initial starting point for the subject matter of metaphysics.