"1337 5p34k" (leet speak) -- basically, use numbers and other alphanumeric characters and symbols instead of letters.  Usually found in chatrooms of 13 yr olds.

I use it because not many people can read it right off.   At work, I posted "P3N15" and no one knew what it meant, save for a few nerds who didn't say anything.

A list of letter and the corresponding number:
Note: Capital letters are the same a lower case.

A -- 4
B -- 8
C -- (
D -- |)
E -- 3
F --
G -- 6, 9
H -- |-|
I -- 1, l
J --
K -- |<
L -- 1, l
M -- /\/\
N -- |\|
O -- 0
P --
Q --
R -- |2
S -- 5, 2
T -- 7
U -- |_|
V -- \/
W -- \/\/
X -- ><
Y --
Z -- 2

Note that I and L are the same. To find out whether the word has an "I" or an "L", just translate the word.
I know I have missed some letters. I have either never seen their 1337 counterpart, or don't remember how it's typed.
This is just what I have seen in chatrooms when I was on IRC and various places on the 'net.

I will almost never type anything in 1337, so don't worry.

Wow!!!
Montreal is warmer than Texas today.
But not for long.

Was your BD yesterday, how could I forget, the same as my baby who turned 9!!!!

Yes some folks do abandon their kids for a new BF
I agree totally with you about pets.

Hi Jodee
Can you make a manip of Sevina and Santa Claus?
See, they were in wizard school together in the old days and are now dating.
shhhhhh.
don't tell anyone
Sevina needs a date for a party this season and she'd like to go with him.