Braille is one of a few systems out there that allow vision-impaired people to be able to read, and by far
the most common. The system involves raised bumps arranged in two columns of three per character.
Most dictionaries and reference books have a listing for Braille. In the standard alphabet, the bumps are arranged such that there is a bump in the top row, and such that there is a bump in the left column. This allows a reader to be able to be sure which character they're reading without any positional context. (If, for example, one encounters a pair of dots in the same row and no others, they must be in the top row; there aren't also other characters that are found in the middle row and bottom rows.)
There is also such a thing as Grade 2 Braille which is far more complex. The standard alphabet, numbers and punctuation are the same, but there is an additional system of two-letter characters, abbreviations and conventions that allow more text to be put into the same space. (Think about it: since the letters are raised dots on the page, there's no such thing as two-sided Braille printing, and the letters have to be large enough to be read with the average-sized fingertip. Braille printing is not very dense.)
When I first heard about Grade 2 Braille, I went out onto the Internet to investigate it, but I had a very difficult time finding any sort of reference to it. These pages are meant to correct some of that.
There are lots of courses and guides you can buy that will allow you to learn Braille, and Grade 2 Braille, if that is your goal. That's not the goal of the pages, however. Everything is graphics-based, and so the usual way that blind people can surf on-line won't even allow them to see most of the content. Since Grade 2 Braille is supposed to be a standard, there's no sensible reason for keeping it secret.
These pages are meant to be a reference for puzzlers or other people interested in this way of expressing language.
First is a chart that lists what values each configuration of dots can have. The graphics there and elsewhere are colour-coded. Red symbols can appear anywhere within a string of Braille characters. Yellow or gold ones must appear by themselves, surrounded by spaces. Green symbols must begin space-delimited strings, blue ones in the middle, and purple ones at the end. These last three are strict descriptions: a character in the middle of a string must have a non-space character before it and after it in its string.
There are also greyed out symbols on black backgrounds. These characters are not interpreted by themselves. One example is at "dots 46" in the fifth row of the chart. Its label is "suffix L1", or suffix level 1. This is purely my own description, not a standard one. That symbol is used internally within Braille words to create suffixes, usually by following it with the last letter of the suffix. [Suffix level 1][S], for example, signifies -less. A chart for these short forms is also available.
Rules pages for how Grade 2 Braille works can be found here.