Complex sentence: Gruber introduced the term to mean a specification of a conceptualization: An ontology is a description (like a formal specification of a program) of the concepts and relationships that can formally exist for an agent or a community of agents.
Split into simpler sentences: Gruber introduced the term to mean a specification of a conceptualization. That is, An ontology is a description (like a formal specification of a program) of the concepts and relationships that can formally exist for an agent or a community of agents.