Web Accessibility (WA) ensures that web sites are usable by people with disabilities who might be accessing the web using Assistive Technologies. Assistive Technologies could be screen readers or input devices other than a standard keyboard and mouse.
To have a web site that is accessibile involves following guidelines and simple rules when creating your site and maintaining content to ensure the greatest number of visitors can use your web site.
An accessible office building with a wheelchair ramp does not have to be less attractive than a non accessible office building that only has steps. Some techniques to improve Web Accessibility actually improve the web site for all users in much the same way that an elevator provides wheelchair access but is used by people of all abilities.