The WAI is a W3C specification providing guidance on accessibility of Web sites for people with disabilities.
It is basically a list of what you should do for your site to make it more accessible to all people.
The long list is broken up into three priority checkpoint levels: Priority 1 which is what every webmaster must do to make websites accessible to all, Priority 2 which is what every webmaster should do in order to aid accessibility issues, and Priority 3 which is what every webmaster may do in order to aid accessibility issues for some. Conformance for the WAI is broken up into three conformance levels: Conformance Level A satisfies all Priority 1 checkpoints, Conformance Level Double-A satisfies all Priority 1 and 2 checkpoints, and Conformance Level Triple-A satisfies all Priority 1, 2, and 3 checkpoints.
I find it's only necessary to have the Conformance Level of Double-A. Conformance Level A is too narrow, and Conformance Level A is much too strict. There is no real valid validator for the WAI, so you'll have to make sure that you are compliant by yourself. A simple checklist for the WAI is available at http://www.w3.org/TR/WCAG10/full-checklist.html
More on the WAI:
- http://www.w3.org/WAI/
- http://www.w3.org/TR/WCAG10/full-checklist.html
- http://www.w3.org/WAI/References/QuickTips/
- http://www.w3.org/1999/05/WCAG-REC-fact