The accessibility Web talks about to the capacity of access to the Web and its contents by all the people independent of the incapacity (physical, intellectual or technical) who present or from that they are derived from the use context (technological or environmental). This quality intimately is related to the usability.
When the websites are designed thinking about the accessibility, all the users can accede in conditions of equality to the contents. For example, when a site has a semantically correct XHTML code, an alternative text is provided equivalent to the images and to the connections a significant name occurs them, this allows usuary the blind ones to use screen readers or lines Braille to accede to the contents. When the videos have subtitles, the users with auditory difficulties will be able to understand them totally. If the contents are written in a simple language and are illustrated with diagrams and animations, the users with dyslexia or problems of learning are in better conditions for understanding them.
If the size of the text is sufficiently great, the users with visual problems can read it without difficulty. In the same way, the size of the bellboys or the active areas adapted can facilitate its use to the users who cannot control the mouse accurately. If the actions are avoided that depend on a concrete device (to press a key, to click with the mouse) the user will be able to choose the device that agrees to him more.