RDFa and microformats - embedding Semantic Web data within HTML Web pages
For all of its raw power, one difficulty with the Semantic Web with its RDF resources is that it is separate from the traditional Web of HTML pages that we all can view and interact with. The only way that you and I can readily access the Semantic Web is if some computer program does the access for us and maps between RDF and HTML or some other format suitable for a user interface. Now comes RDFa, which is an emerging standard for allowing RDF resources to be embedded directly in HTML (or XHTML) Web pages, a hybrid solution designed to provide the best of both worlds. Sometimes the term microformats is used to refer to how RDF resources can be packaged and embedded in Web pages, although microformats are not limited to RDFa.
The initial thrust of RDFa is for XHTML Web pages, but there is an effort underway for HTML web pages as well.
How it all plays out remains to be seen and the effort is still nascent, but does show promise.
OTOH, even success on the RDFa/microformat front will not automatically bridge The Semantic Abyss, but it certainly does help to bridge the gap between the HTML world of the Web and the RDF world of the Semantic Web.
You can read the RDFa Wikipedia article.
You can read the Microformats Wikipedia article.
You can also read the W3C RDFa Primer - Embedding Structured Data in Web Pages.