Braille is essentially a language of raised dots which allow blind people to read using their fingers to feel the patterns formed by the dots. Braille was originally introduced in the Ruby and Sapphire games as a central part to the side quest to gather the Regis. In a way the use of braille in the pokemon games seems to have developed from the use of the Unown in GSC in the Ruins of Alph to solve puzzles.
More specifically, wikipedia refers to braille (in real life) as:
Braille EntryThe Braille system is a method that is widely used by blind people to read and write. Braille was devised in 1821 by Louis Braille, a Frenchman. Each Braille character or cell is made up of six dot positions, arranged in a rectangle containing two columns of three dots each. A dot may be raised at any of the six positions to form sixty-four (26) permutations, including the arrangement in which no dots are raised. For reference purposes, a particular permutation may be described by naming the positions where dots are raised, the positions being universally numbered 1 to 3, from top to bottom, on the left, and 4 to 6, from top to bottom, on the right. For example, dots 1-3-4 would describe a cell with three dots raised, at the top and bottom in the left column and on top of the right column, i.e., the letter m. The lines of horizontal Braille text are separated by a space, much like visible printed text, so that the dots of one line can be differentiated from the Braille text above and below. Punctuation is represented by its own unique set of characters.
Braille is used in a variety of different places inside of Ruby, Sapphire, Emerald, Fire Red, and Leaf Green:
Inside of the Sealed Chamber, Braille is used to spell out messages in several different rooms.
Underwater, in front of the Sealed Chamber:
Go up here
First comes Relicanth. Last comes wailord.
In this cave we have lived.
We owe all to the pokemon.
But, we sealed the pokemon away.
We feared it.
Those with courage, those with hope.
Open a door. An eternal pokemon waits.
Stop and wait. Wait for time to pass twice.
Right, right. Down, down. Then, use strength.
With new time, hope and love, aim to the sky in the middle.
Fire Red/Leaf Green:
Island 1, obtaining the Ruby:
Everything has meaning
existence has meaning
being alive has meaning
Island 6, obtaining the Sapphire:
Bottom Floor of the Dotted Hole
Let the two glittering stones
One in Red One in Blue
Connect the pass.
Two friends sharing power
open a window to a new world that glows
The next world waits for you.