Accessibility has been shortened by Google to just A11y, and it means that sites should be available to everyone, they are sites that are available to anyone, anywhere at anytime on any device. It is interesting to note that accessibility, simply put, is to make the site easy to use for everyone. Users may suffer from a broken wrist, a broken trackpad or just be on a shaky train, either option means a certain difficulty for the user to take advantage of the web. Google uses WCAG (Web Content Accessibility Guidelines) do deliver their content with high importance on access with some countries using their rules as a legal requirement for websites. Use this checklist to ensure the website is WCAG approved;
Input via the keyboard is vital, a user should be able to browse an entire website using the tab, arrow and enter buttons.