From OWL Web Ontology Language Guide ( 2004-02-10) as in RDF
(Ontology terminology) An abstract representation of a concept in a domain as a collection of related classes. For example, a medical model might have protocol, guidelines, and patient data as classes.
A single concept within a classification of knowledge.
A class defines a group of interrelated properties in an ontology. In F-Logic terminology, classes are called concepts.
From RDF Semantics ( 2004-02-10) (n.) A general concept, category or classification. Something used primarily to classify or categorize other things. Formally, in RDF, a resource of type rdfs:Class with an associated set of resources all of which have the class as a value of the rdf:type property. Classes are often called 'predicates' in the formal logical literature.