• Web accessibility is enabling people with all abilities and disabilities have access to services and information on the web.
    It has a great deal to do with best-practice on the web, as many measures taken to ensure accessibility will benefit all users of your website.
    Some of the most basic meaures include making sure the semantics (the logical sequence and structure) of your document is correct and also best practice from W3C and other bodies.
Read the 'Web accessibility' on Wikipedia