down: 1. adj. Not operating. "The up escalator is down" is considered a humorous thing to say,

:down: 1. adj. Not operating. "The up escalator is down" is
considered a humorous thing to say, and "The elevator is down"
always means "The elevator isn't working" and never refers to
what floor the elevator is on. With respect to computers, this
term has passed into the mainstream; the extension to other kinds
of machine is still hackish. 2. `go down' vi. To stop
functioning; usually said of the {system}. The message from the
{console} that every hacker hates to hear from the operator is
"System going down in 5 minutes". 3. `take down', `bring
down' vt. To deactivate purposely, usually for repair work or
{PM}. "I'm taking the system down to work on that bug in the
tape drive." Occasionally one hears the word `down' by itself
used as a verb in this vt. sense. See {crash};
oppose {up}.
-- The AI Hackers Dictionary