Manipulating the keyboard's numerals to write sentences in a wierd hard to read kind of way. Used mainly by computer nerds and losers with too much time on their hands.
2 guys chatting on msn:
Guy1: Hey man how are you?
Guy2: !m 0k $!tt!n @t (-)0m& \/\/@tc(-)!n9 +v, U?
Guy1: Dude I can't read whatever the hell you're trying to say, so quit Key Krunching!