I wouldn't dare try to define 'disability'. Try this page from the DEMOS Disability Awareness module for academic staff, which gives a good overview, or the Disability Rights Commission. There is no world-wide agreement on politically correct wording either, which makes writing about disability issues a walk on a tight-rope. One thing is for sure, however, disability is not the barrier, inaccessible web design is.
Learn about Barriers to access for people with disabilities.
A website or electronic document is accessible when anyone can access the information contained in it, regardless of physical, economic or technological circumstances.
Software or hardware that has been specifically designed to assist people with disabilities. This includes screen readers and magnifiers, speech synthesizers, braille printers, voice input software and hardware such as alternative input devices (alternative keyboards and mice, foot pedals, switches etc.)
A browser is a computer program that opens and displays web pages. Some of the browsers currently in use: Netscape, Opera, Internet Explorer.
The term 'user agent' refers to any software that interprets HTML documents. This includes graphical browsers, text-only browsers and non-visual browsers such as audio or braille browsers.