The Semantic Web is an evolving development of the World Wide Web in which the meaning (semantics) of information and services on the web is defined, making it possible for the web to "understand" and satisfy the requests of people and machines to use the web content.
People can read web pages and understand the meaning of those, but computers can't. So the Semantic Web is trying to read the web pages and extract the meaning from it.
If computers can understand the Web and "read" web pages, it can give us more meaningful information.
If you are interested in the Semantic Web, this article does a really good job on describing what the Semantic Web is all about and how it works.
and here is my bookmark on the Semantic Web: http://www.diigo.com/user/naoyamakino/semanticWeb?tab=250
Kevin Kelly's talk at TED describes only few possibilities of what the Semantic Web could do.
This is pretty cool, and I am looking into that more.