Yahoo! now support “Common Tag” format, an open tagging format developed to make content more connected, discoverable and engaging. Unlike free-text tags, Common Tags are references to unique, well-defined concepts, complete with metadata and their own URLs. With Common Tag, site owners can more easily create topic hubs, cross-promote their content, and enrich their pages with free data, images and widgets. Common Tag ‘s developed by a group of Zemanta, Metaweb, and Yahoo!.

More info: Press Release | Common Tag