Accessibility is a general term used to describe the degree to which a system is usable by as many people as possible without modification. It is not to be confused with 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 and their use of assistive devices such as screen-reading web browsers or wheelchairs. Other meanings are discussed below.

Accessibility is strongly related to universal design in that it is about making things as accessible as possible to as wide a group of people as possible. However, products marketed as having benefited from a Universal Design process are often actually the same devices customized specifically for use by people with disabilities.

Disabilities

The disability rights movement advocates equal access to social, political and economic life which includes not only physical access but access to the same tools, organisations and facilities which we all pay for.

Accessibility is about giving equal access to everyone.

While it is often used to describe facilities or amenities to assist people with disabilities, as in "wheelchair accessible", the term can extend to Braille signage, wheelchair ramps, audio signals at pedestrian crossings, walkway contours, website design, and so on.

Various countries have legislation requiring physical 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.
• In Ontario, Canada, the Ontarians with Disabilities Act of 2001 is meant to "improve the identification, removal and prevention of barriers faced by persons with disabilities..."