The Braille Alphabet is a form of written communication to help blind people read.
It uses a system of raised dots that represent letters of the alphabet. For example, the letter A is represented by one dot in the upper hand left corner of a matrix of six dots in two rows of three.
The letters a through i are written the same as numbers 1 through 9, so a special character is used to show that numbers are used.
The person who invented the Braille Alphabet, Louis Braille, was blinded by a stitching awl in his father's harness-making shop at three years old. He went to a school and managed to learn very well, even earning a scholarship in the Royal Institute for Blind Youth.
While still a student, he started developing the Braille system based on another person's number-letter system.
His system was very successful, and even though he had a music hobby, he continued developing his system for the rest of his life.