Liquid Layouts design is a process of web design and development without resorting to the use of HTML tables for page layout control purposes. Instead of HTML tables, style sheet languages such as CSS are used to arrange elements and text on a web page. CSS was introduced by the World Wide Web Consortium (W3C) to improve web accessibility and to make HTML code semantic rather than presentational.
The best example of tableless web design is CSS Zen Garden (http://www.csszengarden.com/), a site where the same semantic XHTML is shaped in different and unique ways with different CSS. The result is pages that look very different but have the same core content. (Source: http://www.w3.org/Style/CSS/)