A person who is either
experienced or new in the ways of hacking, cheating, or doing things his own way (Oftenly, this way the H4xx0r uses is considered morally wrong or low).
The term "h4xx0r" can be used in both a positive and negative way. Typically, calling someone a h4xx0r is in the negative sort. But some h4xx0rs take pride in being what they are, just like nerds.
H4xx0r, is basically a computer-experienced person's/gamer's way of calling someone a hacker.
If h4xx0r is spelt with one or two big X's, that is the
final form of the word and
the highest degree.
h4xx0r, h4xX0r, h4XX0r.