Introduction to web content accessibility
From Joomla! Documentation
Consider your audience... they may not be able to see, hear or move, they may have a text only browser or an older browser. Accessibility standards are designed to make web sites usable for these people and it's becoming increasingly important that Web designers and developers take note of their requirements. In fact in certain countries it's a legal requirement whilst in others there are legal precedence for the requirement of accessible web sites.