The Web is fundamentally designed to work for all people, whatever their hardware, software, language, location, or ability. When the Web meets this goal, it is accessible to people with a diverse range of hearing, movement, sight, and cognitive abilities.
Thus the impact of disability is radically changed on the Web because the Web removes barriers to communication and interaction that many people face in the physical world. However, when websites, applications, technologies, or tools are badly designed, they can create barriers that exclude people from using the Web.
Accessibility is essential for developers and organizations that want to create high-quality websites and web tools, and not exclude people from using their products and services.

https://www.w3.org/standards/webdesign/accessibility