RDFa (Resource Description Framework in attributes) is a specification that allows web developers to embed rich metadata within HTML documents. This metadata helps search engines and other applications understand the content of a webpage better, improving data interoperability and enhancing search results. By using RDFa attributes, developers can annotate elements in their HTML with structured data, linking them to specific concepts or entities. This makes it easier for machines to process and utilize the information, ultimately leading to more meaningful and relevant online experiences for users.