Web accessibility means that people with disabilities can use the Web. More specifically, Web accessibility means that people with disabilities can perceive, understand, navigate, and interact with the Web, and that they can contribute to the Web. Web accessibility also benefits others, including older people with changing abilities due to aging.
Drupal for accessibility:-
This initiative started with advancements with Drupal 7 accessibility.
If you rely on a screen reader or other assistive technology, you will be glad to know that Drupal built has to encourage and support the proper use of semantic markup.
For example, you should be able to use headings reliably for page-level navigation.