Orthography
One of the hallmarks of leet is its unique approach to orthography, using substitutions of other characters, letters or otherwise, to represent a letter or letters in a word. For more casual use of leet, the primary strategy is to use homoglyphs, symbols that closely resemble (to varying degrees) the letters for which they stand. The symbol chosen is flexible—anything that the reader can make sense of is valid. However, this practice is not extensively used in regular Leet; more often it is seen in situations where the argot (i.e., "secret language") characteristics of the system are required, either to exclude newbies or outsiders in general, i.e., anything that the average reader cannot make sense of is valid; a valid reader should himself try to make sense, if deserving of the underlying message. Another use for Leet orthographic substitutions is the creation of paraphrased passwords. By using this method, one can create a relatively secure password which would still be easily remembered. Limitations imposed by websites on password length (usually no more than 36) and the characters permitted (usually alphanumeric and underscore) requires less extensive forms of Leet when used in this application.
Some examples of leet include B1ff and n00b, a term for the stereotypical newbie; the l33t programming language; and the webcomic Megatokyo, which contains characters who speak leet.
Read more about this topic: Leetspeak