In this paper the role of ontology is considered in the context of information systems and conceptual modelling. Firstly we describe information systems and conceptual modelling without using the word “ontology”. Then two senses of ontology are presented: philosophical and knowledge representation views. In this connection both Gruber's and Guarino's definitions of “ontology” are scrutinized. It is proposed that the kind of terminological shifts concerning the word “ontology”, and practiced e.g. by Gruber and Guarino, have caused more confusion than clarification in the field of information systems and conceptual modelling. Instead of given a new or a better definition of our own, our view is that the word “ontology” should be used in its traditional philosophical sense only, whereas our aim in the field of information systems and conceptual modelling is to reach conceptual clarity.