Accessibility, or universal design, is concerned with ensuring that users with diverse needs are able to access information through a variety of methods. Anti discrimination laws require accessibility be considered.
Accessibility has come to the fore in web design in recent years. W3C guidelines exist that can be used to verify that information is presented according to universal design principles.
I have been following accessible guidelines in my websites since I first learnt HTML, through simple methods like alt attributes for images and clear page structure. Working for Education Queensland brought web accessibility to the fore.