Full Idea
In 'Metaphysics' Aristotle characterises metaphysics in three ways: as the science of the first or ultimate explanation of things; as the science of being qua being; and the science of primary being ('ousia').
Gist of Idea
Metaphysics is the science of ultimate explanation, or of pure existence, or of primary existence
Source
report of Aristotle (Metaphysics [c.324 BCE], book) by Vassilis Politis - Aristotle and the Metaphysics 2.1
Book Reference
Politis,Vasilis: 'Aristotle and the Metaphysics' [Routledge 2004], p.29
A Reaction
I am a bit baffled about how anything worthwhile can be said about 'being qua being', but the other two seem worth pursuing, and may boil down to the same thing.