Accessibility is a general term used to describe how easy it is for people to get to, use, and understand things. It is not to be confused by Usability which is used to describe how easily a thing can be used by any type of user. One meaning of accessibility specifically focuses on people with disabilities, but there are other meanings discussed below.

Disabilities

Accessibility is most often used to describe facilities or amenities to assist people with disabilities, as in "wheelchair accessible". This can extend to Braille signage, wheelchair ramps, audio signals at pedestrian crossings, walkway contours, website design, and so on. The disability rights movement advocates for more accessibility.

Various countries have legislation requiring accessibility:

• In the UK, the Disability Discrimination Act 1995 has numerous provisions for accessibility
• In the US, under the Americans with Disabilities Act of 1990, new public and private business construction generally must be accessible. Existing private businesses are required to increase the accessibility of their facilities when making any other renovations in proportion to the cost of the other renovations. The U.S. Access Board is "A Federal Agency Committed to Accessible Design for People with Disabilities." Many states in the US have their own disability laws.

Transportation

In transportation, accessibility refers to the ease of reaching destinations. People who are in places that are highly accessible can reach many other activities or destinations quickly, people in inaccessible places can reach many fewer places in the same amount of time.

A measure that is often used is to measure accessibility in a traffic analysis zone i is:

where:

• i = index of origin zones
• j = index of destination zones
• f(C_ij) = function of generalized travel cost (so that nearer (or less expensive) places are weighted more than farther or more expensive places).

Art and entertainment

Pieces of music, novels, and other works of art are commonly judged on their accessibility, with some feeling that less-accessible works are superior and some considering them inferior. For instance, serial music is often valued by its creators and others for its high concentration of information while being criticized by Fred Lerdahl and others for being literally unintelligible.

See also Computer accessibility and Assistive technology.