Leet (meaning 'elite', most commonly represented as 1337) is an online culture or attitude sometimes identified by frequent use of leetspeak (a spelling convention for typed words).

The word itself is derived phonetically from the word "elite", and is a cipher, or cryptic form of English spelling. The convention was intended principally to bypass automatic text parsers, perhaps because the originators of the convention felt they were under some form of surveillance, or desired for other reasons to have private conversations in public spaces. Hence the term elite, as only those 'in the know' could easily read what was said.

The spelling convention of leetspeak is characterized by the use of non-alphabetic characters to stand for letters which bear superficial resemblance, as well as by a number of spelling changes such as the substitution of "z" for for the "s" at the end of a plural word and "x" for "(c)k" or "(c)ks." Letters may be chosen as substitutes for other letters, based on visual similarity. Leetspeak was probably first used by hackers on Bulletin Board Systems, and then later adopted by users of Online Multiplayer Games and other Internet communities.

Spellings do not always follow a set convention. The same word may be spelled differently by different people, or indeed by the same person. This is symptomatic of the desire or affected desire to elude comprehension by others unfamiliar with the art form.

Leetspeak is not popular among all hackers, and nowadays is most commonly used in an ironic manner to represent immaturity or to annoy people. Many consider it a pointless affectation, and as it has become widely used it is less useful as a way of showing membership of an "elite" group. It is nonetheless a cultural phenomenon well known amongst hackers and many other Internet users, especially gamers.

Certain factions maintain that "true" leetspeak is spelled correctly, with the exceptions described above. They do not consider the use of extreme short forms (such as "b" for "be", or "u" for "you") as leetspeak; instead, they refer to it by such terms as "AOL speak". This is because they associate such habits with users who use ISPs like AOL, which is associated with "noobiness" and therefore not considered "elite". The chief difference between leetspeak and AOL speak is that leetspeak has the goal of obfuscating traditional written language while in AOL speak the goal is primarily to shorten words (and therefore allow "n00bs" to be able to communicate more quickly). Another convention sometimes associated with leetspeak or Internet chatting is capitalizing every other letter (LiKe ThIs), sometimes called studlycaps or stickycaps. A similar habit involves capitalizing every consonant (LiKe THiS).

taken from wikipedia. good explanation.
here

they even have tables for decoding :lmao: