Aristotle described ontology as "the science of being qua being." The word 'qua' means 'with regard to the aspect of'. According to this theory, then, ontology is the science of being with regard to the aspect of being, or the study of beings insofar as they exist. More precisely, ontology concerns determining what categories of being are fundamental and asks whether, and in what sense, the items in those categories can be said to "be."
Different philosophers make different lists of the fundamental categories of being; one of the basic questions of ontology is: "What are the fundamental categories of being?"
Here are a few more examples of ontological questions:
A few quintessential ontological concepts are:
External Links Aristotle's definition of a science of Being qua Being: ancient and modern interpretations (http://www.formalontology.it/being-qua-being.htm)