System of characters for the blind; developed by Louis Braille. For many languages and special languages (e.g. mathematics, music) there are separate subsets. The individual characters are shown in a grid of three points (height) by two points (width). Braille output via computer is realized with Braille displays. Braille displays use two additional points, because more signs are necessary for computer-related tasks than can be shown with six points. The grid is thus extended to four (height) by two (width) points. A precondition for a faultless output of texts and other contents on Braille displays (or screen readers) are barrier-free GUIs and documentations.