Joomla! Documentation™

Web Accessibility is based around maintaining certain techniques in the design of a web page so as to allow people with disabilities to easy access the information contained on the page. Some of the things that effect accessibility include markup, use of javascript, image and media usage as well as basic layout techniques.

Consider your audience... they may not be able to see, hear or move, they may have a text only browser or and older browser. Accessibility standards are designed to make web sites usable for these people and its increasingly becomeing important that Web designers and developers take note of their requirements. In fact in certain countries its a legal requirement whilst in some others there are legal precedence for the requirement of accessible web sites.