Reference Concepts are a distinct subset of the more broadly understood concept such as used in the SKOS RDFS controlled vocabulary or formal concept analysis or the very general or abstract concepts common to some upper ontologies.
Reference Concepts are selected for their use as concrete, subject-related or commonly used notions for describing tangible ideas and referents in human experience and language. Reference Concepts are classes, the members of which are nameable instances or named entities, which by definition are held as distinct from these concepts. The UMBEL ontology is a coherently organized structure (or reference "backbone") of these Reference Concepts.