adj. Describes a condition of suspended animation in which something is so wedged or hung that it makes no response. If you are typing on a terminal and suddenly the computer doesn't even echo the letters back to the screen as you type, let alone do what you're asking it to do, then the computer is suffering from catatonia (possibly because it has crashed).
"There I was in the middle of a winning game of nethack and it went catatonic on me! Aaargh!"