Originally Posted by Wikipedia

Leet (often also leetspeak or 1337) from the phonetic form of the word "elite", is a cipher, or novel form of English spelling. It is characterized by the use of non-alphabet characters to stand for letters bearing a superficial resemblance, and by a number of spelling changes such as the substitution of "z" for final "s" and "x" for "(c)ks". Leetspeak is traditionally used on the Internet and other online communities, such as bulletin board systems. Leetspeak is used by hackers, script kiddies, gamers and lamers.