What is "accessibility"

It refers to the inclusive practice of developing web content that can be used by all persons being disabled or not.

The needs that web accessibility intends to address include: visual, motor or mobility impairments (for example difficulty or impossibility of using the hands), hearing, convulsions (such as visual seizure caused by stroboscopic or "blinker" effects), cognitive or intellectual (developmental disabilities or learning difficulties such as dyslexia, for example).

Related: WCAG (Web Content Accessibility Guidelines), project created by WAI (Web Accessibility Initiative) and W3C (World Wide Web Consortium), which contains the definitive guidelines on how to create widely accessible web content based on a set of technologically neutral guidelines for accessibility on the Internet.