‘l33t speak’ is an Internet-based language reliant on the keyboard. It is, however, simple to learn and has much room for creativity.

Some Examples:

     * 0w|\| or 0wn3d - One of the most popular l33t words it is very loosely defined as beaten or can simply be an expression of awe, for example, ‘I 0wn3d you’ means ‘I have beaten you in a very humiliating fashion’, or ‘0wn4ge!’ which means ‘That was (or is) very nifty’.
    * 13wt - Treasure, good merchandise, possessions, a misspelling of loot. Most commonly referring to pirated software, items in a game or promotional giveaways.
    * h4x0r - Hacker, can be used for a real hacker or simply a very skillful person. This is the most common occurrence of the -0r clause.
    * ph33r - Fear, most commonly used in such phrases as, ‘Ph33r m3!’ or ‘Ph33r |\/|y 1337 sk1llz!’ It can also be written as, ‘ph34r’.
    * sk1llz - Obviously derived from ‘skill’, referring to skill in some type of online game, programming or hacking. Many times used in conjunction with ‘m4d’. As a general rule, if one has sk1llz, one is to be ph33r3d.
    * m4d - Mad, mostly used as a descriptive term meaning great, for example, ‘h3s g0t m4d sk1llz’.
    * f00 - Fool, one who isn’t very bright or skillful.
    * d00d - Dude; an expression of comrade, or just used to address a random person online.

Source: BBC