Hexspeak

Hexspeak, like leetspeak, is a novelty form of variant English spelling using the hexadecimal numbers. Created by programmers who wanted a magic number, hexspeak words can serve as a clear and unique identifier with which to mark memory or data.

Using hexadecimal notation, which includes the digits 0123456789ABCDEF, it is possible to spell several words. Further words can be made by treating some of the decimal numbers as letters - the digit "0" can represent the letter "O", and "1" can represent the letters "I" or "L". Less commonly, "5" can represent "S", "7" represent "T", "12" represent "R" and "6" or "9" can represent "G" or "g" respectively. Numbers such as 2 or 8 can be used in a manner similar to leet or rebuses; e.g. the word "defecate" can be expressed either as DEFECA7E or DEFEC8. (2 bears a resemblance to Z, but because that letter is the least used in the English language, such a usage is very rare.)

Read more about Hexspeak:  Notable Magic Numbers, Alternative Letters