Short for elite (31337), which is the UDP (User Datagram Port) used by a hacker group called the Dead Cow Cult.
1337 is simply a language of symbols that look similar to the english alphabet.
Using this system,
L Replacing an english letter
S Replacing a leetian symbol
here is a list of the leetian characters.
Notice their similarities to the alphabet.
"/\/" looks kind of like "N" and,
"\/" looks kind of like "V."
It's not too complicated. I'm confident anyone can learn. Please use it wisely though, for I hate when it substitutes that which should simply be english. Maybe google will add it to their Translator in Language Settings...
(use it to confuse old people)