To enable persons with disabilities to live independently and participate fully in all aspects of life, States Parties shall take appropriate measures to ensure to persons with disabilities access, on an equal basis with others, to the physical environment, to transportation, to information and communications, including information and communications technologies and systems, and to other facilities and services open or provided to the public, both in urban and in rural areas.
Source: Convention on the Rights of Persons with Disabilities (http://www.un.org/disabilities/convention/conventionfull.shtml)
Accessibility [...] is defined as meaning that people with disabilities have access, on an equal basis with others, to the physical environment, transportation, information and communications technologies and systems (ICT), and other facilities and services in line with the UN Convention on the Rights of Person with Disabilities.
Source: European Accessibility Act: legislative initiative to improve accessibility of goods and services in the Internal Market (http://ec.europa.eu/smart-regulation/impact/planned_ia/docs/2012_just_025_european_accessibiliy_act_en.pdf)
Accessibility is the degree to which a product, device, service, or environment is available to as many people as possible. Accessibility can be viewed as the "ability to access" and benefit from some system or entity. The concept often focuses on people with disabilities or special needs (such as the Convention on the Rights of Persons with Disabilities) and their right of access, enabling the use of assistive technology.
Source: Wikipedia (http://en.wikipedia.org/wiki/Accessibility)