UMBEL is a lightweight ontology and subject concept framework comprised of around 20,000 concepts and their relationships that aims to provide context for web content and datasets. It serves as a reference structure for placing information into context with other data by defining common subject concepts and mapping entities and datasets to these concepts. UMBEL is freely available under an open source license and relies on existing vocabularies and ontologies like SKOS, RDFS, and OWL to provide interoperability.