Web accessibility is the practice of removing any barriers to interaction with technology for anyone, including people with disabilities. Simply put, this means that when you create an application or a website, everyone should be able to access it.
The Supreme Court recently determined that the Internet is public domain; therefore, it must be accessible to everyone (according to regulations that govern accessibility in the United States: Section 508 and the American with Disabilities Act), including people with disabilities, which can include visual, physical, auditory, speech, or cognitive impairments. It is important that web developers conform to standards of web accessibility while developing a website or working on digital marketing material.
The article, “What Developers Should Know For A Universally Accessible Internet” on Knowbility’s blog Universally Designed is a great start for beginner’s web accessibility guidelines: read it here.