The Metaphysic or Metaphysics is a canonical collection of various writings by Aristotle which were collected and featured in the order they now appear, although there are historical-critical debates about whether this was the original intended format for the works, whether this was the original arrange of them and perhaps most concerning, whether Aristotle is even the author of the work in its entirety or at all. But, although academic debate continues on the issues, the important fact of the matter is that the arrangement that we now have is historically important in the bedrock of Western thought, and the work is historically attributed to Aristotle.
After the fall of Greece, many writings were confiscated or burned and many were re-discovered by Islamic nations who translated them and reintroduced them to the Western world after many years where Aristotle was not readily available. Since many works that were available in the West referrenced Aristotle's writings as authoritative and helpful, the reintroduction of the Metaphysics and many others spurred a philosophical revolution which laid the foundation for the French Renaissance.
The work is offered as a collection of related arguments thematically centered around the "first philosophy," which is the philosophy governing truths that were not physical or natural. The natural sciences were discussed by Aristotle as the "second philosophy." Aristotle's understanding is often contrasted with that of Plato, whose philosophy is generally governed by his belief in transcendental forms which were the basis for the existence of the physical world.
Aristotle by contrast concedes that the metaphysical world is real and important, but philosophy ought not to be governed by hypotheses about metaphysical truths, but rather through inference based on observable truths. This doesn't render his philosophy naturalistic, but it does change his conclusions in an important schematic way. Aristotle is considered as a forefather of philosophy and still remains authoritative in syllogistic philosophy despite having written thousands of years ago.