Paul,
W3C is an acronym,of sorts, for the World Wide Web Consortium. They have become the official standards body for the web - as far as anything on the web is official.
The web really started at CERN (European Nuclear Research Centre) as a means of disseminating scientific papers. W3C is a CERN spin-off that monitors and advises on web standards. They produce papers proposing standards to which all kinds of media producers working for the web should adhere.
Their standards work is especially important for some web platforms. For example, mobile phones often need web pages that are strictly XHTML (Extended Hypertext Markup Language) and pages that are not will fail to display. I run
a web site, ([url=http://yaws.mobi]http://yaws.mobi), for recreational pilots[/url] needing airfield weather information on their mobiles, and know to my cost the headaches of making sure that everything conforms to standards.
Not surpringly W3C have a web site
http://www.w3.org/.
Hope this potted guide works for you.
Angela