Web standards are the rules and specifications for creating web pages and web interfaces.
Web standards are the technical specifications that dictate how HTML, XML, CSS, XHTML and other technologies used to build web pages should be used, how they should be coded, and how they should be interpreted.
The web standards are the underlying rules of the internet. Building your web site in line with these standards will help address accessibility and browser compatibility, and will help insure that your web site will continue to work correctly for new versions of web browsers. Building a web site that is standards compliant will also insure that the search engines can access all of your site and can index it properly, and this can have a significant positive impact on SEO (search engine optimization).
Insuring that your web site complies with the web standards also means not having to re-code your web site for new ways to access the web, such as netbooks and smart phones, or whatever comes out next. Any organization is concerned about their site being standards compliant, unless they have an unlimited budget.