The semantic web is a way of representing information on the web such that machines can understand it and the relationships among different pieces of data. Much as hyperlinks revolutionized the web for humans, the semantic web, although seemingly a simple thing at first glance, is likely to create another revolution in the web.
Computers can easily infer information, tailor search results more intelligently, and generally perform more complex tasks with the data of the web once it is formatted in a way that the machines can easily read. See the Wikipedia entry on Semantic Web for more information. The image above shows how many different repositories of information are now linked thanks to the different semantic web projects now in existence. DBpedia, at the center, is particularly noteworthy because allows far more complex and nuanced queries of the massive amounts of information already in Wikipedia.
This group, then, is for anyone who wants to learn more about the semantic web, discuss tools, practices, ontologies, or collaborate on semantic web projects.