Complex sentence: In computer science and information science, an ontology is a formal naming and definition of the types, properties, and interrelationships of the entities that really or fundamentally exist for that domain.
Split into simpler sentences: In computer science and information science, an ontology is a formal framework for representing information about a particular domain of discourse. It names and defines the types, properties, and interrelationships of the entities that really or fundamentally exist for that domain.