ontology

Noun C1 – Advanced

The branch of philosophy concerned with the nature of being and existence, or, in computing, a formal structure describing the categories and relationships within a subject.

"Her thesis explores the ontology of digital objects, asking whether a computer file truly exists the way a physical book does."

'Ontology' has a second, unrelated technical sense in computer science, where it means a structured map of categories and how they relate to each other.