Web Content Accessibility Guidelines (WCAG) are part of a series of Web accessibility guidelines published by the W3C's Web Accessibility Initiative. They consist of a set of guidelines on making content accessible, primarily for disabled users, but also for all user agents, including highly limited devices, such as mobile phones.
The guidelines have three priority levels:

Accessible Web design is the art of creating webpages that are accessible to everyone, using any device. It is especially important so that people with disabilities - whether due to accident, disease or old age - can access the information in Web pages and be able to navigate through the website.