Ontology

Ontology (from onto-, from the Greek ὤν, ὄντος "being; that which is", present participle of the verb εἰμί, eimi "be", and -λογία, -logia: "science, study, theory") is the philosophical study of the nature of being, existence, or reality, as well as the basic categories of being and their relations. Traditionally listed as a part of the major branch of philosophy known as metaphysics, ontology deals with questions concerning what entities exist or can be said to exist, and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and differences.