  In the knowledge engineering community "ontology" is usually defined in the
tradition of Gruber as an "explicit specification of a conceptualization".
Several variations of this definition exist. In the paper we argue that (with
one notable exception) these definitions are of no explanatory value, because
they violate one of the basic rules for good definitions: The defining
statement (the definiens) should be clearer than the term that is defined (the
definiendum). In the paper we propose a different definition of "ontology" and
discuss how it helps to explain various phenomena: the ability of ontologies to
change, the role of the choice of vocabulary, the significance of annotations,
the possibility of collaborative ontology development, and the relationship
between ontological conceptualism and ontological realism.
