“In AI, an ontology is a specification of the meanings of the symbols in an information system. That is, it is a specification of a conceptualization…[it] often involves a community to agree on the meanings of symbols….
… an ontology consists of a vocabulary of the categories of the things (both classes and properties) that a knowledge base may want to represent; ….an organization of the categories...; and a set of axioms restricting the meanings of some of the symbols to better reflect their meaning… ultimately, the relationships are grounded out into primitive...”
Artificial Intelligence: foundations of computational agents, Cambridge University Press, 2017, Sec. 13.3. the 2nd Edition