Web accessibility, or eAccessibility, is the inclusive practice of ensuring there are no barriers that prevent interaction with, or access to, websites on the World Wide Web by people with physical disabilities, situational disabilities, and socio-economic restrictions on bandwidth and speed. When sites are correctly designed, developed and edited, more users have equal access to information and functionality.

For example, when a site is coded with semantically meaningful HTML, with textual equivalents provided for images and with links named meaningfully, this helps blind users using text-to-speech software and/or text-to-Braille hardware. When text and images are large and/or enlargeable, it is easier for users with poor sight to read and understand the content. When links are underlined (or otherwise differentiated) as well as colored, this ensures that color blind users will be able to notice them. When clickable links and areas are large, this helps users who cannot control a mouse with precision. When pages are not coded in a way that hinders navigation by means of the keyboard alone, or a single switch access device alone, this helps users who cannot use a mouse or even a standard keyboard. When videos are closed captioned, chaptered, or a sign language version is available, deaf and hard-of-hearing users can understand the video. When flashing effects are avoided or made optional, users prone to seizures caused by these effects are not put at risk. And when content is written in plain language and illustrated with instructional diagrams and animations, users with dyslexia and learning difficulties are better able to understand the content. When sites are correctly built and maintained, all of these users can be accommodated without decreasing the usability of the site for non-disabled users.

The needs that web accessibility aims to address include:

• Visual: Visual impairments including blindness, various common types of low vision and poor eyesight, various types of color blindness;
• Motor/mobility: e.g. difficulty or inability to use the hands, including tremors, muscle slowness, loss of fine muscle control, etc., due to conditions such as Parkinson's disease, muscular dystrophy, cerebral palsy, stroke;
• Auditory: Deafness or hearing impairments, including individuals who are hard of hearing;
• Seizures: Photo epileptic seizures caused by visual strobe or flashing effects.
• Cognitive and intellectual: Developmental disabilities, learning difficulties (dyslexia, dyscalculia, etc.), and cognitive disabilities (PTSD, Alzheimer's) of various origins, affecting memory, attention, developmental "maturity", problem-solving and logic skills, etc.

Accessibility is not confined to the list above, rather it extends to anyone who is experiencing any permanent, temporary or situational disability. Situational disability refers to someone who may be experiencing a boundary based on the current experience. For example, a person may be situationally one-handed if they are carrying a baby. Web accessibility should be mindful of users experiencing a wide variety of barriers. According to a 2018 WebAIM global survey of web accessibility practitioners, close to 93% of survey respondents received no formal schooling on web accessibility.