Definition of Web Accessibility
Web accessibility refers to the inclusive practice of removing barriers that prevent interaction with or access to websites, by people with disabilities. When sites are correctly designed, developed, and edited, all users have equitable access to information and functionality.
Definition of Disability
U.S. Federal Law defines a disability as a physical or mental impairment that substantially limits one or more of the major life activities of such individual, a record of such an impairment, or being regarded as having such an impairment.
An Accessible Approach
Accessibility focuses on how a person with a disability accesses or benefits from a site, system, or application. Accessibility is an important part of designing your site and should be considered throughout the development process. Section 508 is the governing principle, and it requires that all government information be accessible to users with disabilities.
Accessible sites present information through multiple sensory channels, such as sound and sight, and they allow for additional means of site navigation and interactivity beyond the typical point-and-click-interface: keyboard-based control and voice-based navigation. The combination of a multisensory approach and a multi-interactive approach allows users with disabilities to access the same information as nondisabled users.
Source: usability.gov - https://www.usability.gov/what-and-why/accessibility.html