https://en.wikipedia.org/wiki/Braille

Braille is a tactile writing system and is used by the blind and severely visually impaired, as they cannot read blackletter or can read it only with difficulty. It was developed by Frenchman Louis Braille in 1825. The script consists of dot patterns that are usually pressed into paper from behind and can be felt as raised areas in the front with the fingertips.

A dot grid of 3×2 dots is used to encode letters and groups of letters. The six dots can be used to represent 64 different characters. To extend the character range, for example, upper and lower case, special characters are defined, pointing out corresponding switches or double assignments.

Above the 26 letters of the Latin alphabet as well as the 10 digits, additional letters and letter combinations have been defined depending on the language.