CSS: CSS is an acronym which stands for "cascading Style Sheets". CSS refers to a method of adding styles of web documents. By using external CSS files, a user can easily change the design of many pages by editing one file.

Technically, CSS is a style sheet language, a computer language used to express the presentation of structured documents. While CSS is often used to redesign sites written in HTML and XHTML markup languages, it can also be used in XML documents, including those written in SVG and XUL. This language is used primarily to separate a document's content from it's presentation, changing elements such as the layout, colors and font without altering the information itself.

CSS specifications are regulated by the World Wide Wide Consortium (WC3). However, the language itself was invented by Håkon Wium Lie, a Norwegian web developer, who worked with Tim Berners-Lee, the creator of the world wide web at CERN. Additional work was also performed by Bert Bos, a Dutch computer scientist. Bos currently serves as the WC3's Staff Contact for CSS. Lie, in contrast, went on to become a politician and Chief Technology Officer at a software company.