RDFa

RDFa or Resource Description Framework in Attributes[1] is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within Web documents. The Resource Description Framework (RDF) data-model mapping enables its use for embedding RDF subject-predicate-object expressions within XHTML documents. It also enables the extraction of RDF model triples by compliant user agents. https://en.wikipedia.org/wiki/RDFa

Linked Data in HTML: RDFa is an extension to HTML5 that helps you markup things like People, Places, Events, Recipes and Reviews. Search Engines and Web Services use this markup to generate better search listings and give you better visibility on the Web, so that people can find your website more easily. https://rdfa.info/

https://www.w3.org/MarkUp/2004/rdf-a