SKOS

Simple Knowledge Organisation System or SKOS is

a family of specifications, intended to standardize expressing controlled vocabularies (eg. taxonomies, thesauri, ...) in RDF.
developed and maintained the W3C Semantic Web Deployment Working Group (SWDWG)
described in the SKOS reference (Last Call Working Draft, dated 29 Aug 2008)
to become a W3C Recommendation in the near future.