cascading style sheets (CSS)

A format used to separate style from structure on Web pages, it is a feature of HTML that gives both Web developers and users more control over how Web pages are displayed. 

With CSS, designers create style sheets that define how different elements, such as headers and links, will appear. These style sheets can then be applied to any page or all pages on a particular Web site, which makes coding much easier.

Historical persepective: The term "cascading" derives from the fact that multiple style sheets can be applied to the same Web page. CSS was developed by the W3C; however, this specification continues to evolve and is not fully supported by all Web browsers.