The class skos:Concept is the class of SKOS conceptual resources.
A conceptual resource can be viewed as an idea or notion; a unit of thought. However, what constitutes a "unit of thought" is subjective, and this definition is meant to be suggestive, rather than restrictive.
SkosDesign/ConceptSemantics - W3C Semantic Web Deployment Wiki(About) So, for a resource of type skos:Concept, any properties of that resource (such as creator, date of modification, source etc.) should be interpreted as properties of a concept, and not as properties of some 'real world thing' that that resource may be a conceptualisation of