The study of the most fundamental questions, in particular what there is (ontology),
what is knowledge (epistemology), and what
one should do (ethics)/(morals).
The term metaphysics arose by accident, in that Aristotle
wrote a text on what he called "primary philosophy", which was placed by his
editors after a text on physics, and "after" in Greek is "meta".
The reason the stated questions are fundamental is that some sort of answer
to these questions are presupposed in anything a human being does or thinks
consciously, even if he is not aware of this, or doesn't care whether this is