Words that use other characters. Tend to become very annoying. Here's a list of what each letter is substituted by, usually.
A = 4 or @
B = l3
C = (
D = cl, or |)
E = 3
F = Nothing for F, but you can use ones from different types of languages. Such as ㅋ, which is from Korean alphabet(hangul)
G = 9
H = |-|
I = !, or 1
J = nothing for J
K = l<,
L = |_
M = lVl
N = lV
O = 0
P = not that i know of
Q = still nothing that i know of
R = i got nothing
S = 5
T = +, or 7
U = |_|
V = \/
W = \/\/
X = i got notin
Y = >-
Z = still notin