The general goal of the World Wide Web Consortium (W3C) is to make the Web available to everyone, regardless of the device, platform, network, culture, geographic location, or physical or mental ability of those using it. Collectively, this is known as universality. To ensure these goals are met, the W3C has many initiatives, such as the Internationalisation (I18n) Activity, the Device Independence group, and the Web Accessibility Initiative (WAI).
Author: Gez Lemon
The WAI's role is to ensure that the web is accessible to people with disabilities:
The Web Accessibility Initiative (WAI) works with organizations around the world to develop strategies, guidelines, and resources to help make the Web accessible to people with disabilities.
In a perfect world, just following web standards should be enough to ensure that content is available for everyone. Unfortunately, authors can inadvertently introduce accessibility barriers without realising it. An accessibility barrier is anything that provides a barrier to people with disabilities. A simple example of an accessibility barrier might be where authors decide they don't like the dotted border around active links, and remove it with scripting:
<a href="a.html" onfocus="if(this.blur)this.blur()">
If the above technique is applied to all links in the document, the result is to completely disable keyboard navigation through the links. With this particular example, it's not just accessibility that is effected, it also has an effect on device independence.
Other examples of accessibility barriers may have no effect on device independence, but cause problems for people with disabilities. That is what web accessibility is about; ensuring that people with disabilities do not encounter barriers through things that they cannot readily change. As developers, we all understand the importance of universality to reach and serve the widest possible audience. That is our goal, of which accessibility is an important part of reaching that goal.