HTML stands for HyperText Markup Language. It is used to describe the structure of the information on web pages.

A very simple example, taking a classic newspaper article style layout, this will probably consist of a main heading, a sub heading, several paragraphs of text and the writers name at the end. Each of these “chunks” of text will need to look different. The sub heading will be bigger then the main paragraph of text, the main heading even bigger still etc.

These elements will be marked up using HTML to distinguish between the different content types by wrapping each element inside an HTML tag, which can then have style information applied to them using CSS, such as displaying all main headings in a certain font and colour for example.

XHTML stands for Extensible HyperText Markup Language and is a more recent development on the HTML format, extending it’s abilities, whilst at the same time refining it and making it more compliant.