The term "web standards" can mean different things to different people. For some, it is 'table-free sites', for others it is 'using valid code'. However, web standards are much more than that. A site built to web standards should adhere to standards (HTML, XHTML, XML, CSS, etc) and pursue best practices (valid code, accessible code, semantically correct code, user-friendly URLs, etc).
In other words, a site built to web standards should ideally be lean, clean, CSS-based, accessible, usable and search engine friendly.