back up

(idiomatic, intransitive) To move backwards, especially for a vehicle to do so.
(idiomatic, transitive) To move a vehicle backwards.
(idiomatic, intransitive) To undo one's actions.
(idiomatic, intransitive) To reconsider one's thoughts.
(idiomatic, transitive) To copy (data) so that it can be restored if the main copy is lost.
(idiomatic, transitive) To provide support or the promise of support to.
(idiomatic, intransitive) For the non-striker to take a few steps down the pitch, in preparation to taking a run, just as the bowler bowls the ball.
(idiomatic, intransitive) For a fielder to position himself behind the wicket (relative to a team-mate who is throwing the ball at the wicket) so as to stop the ball, and prevent overthrows.
(idiomatic, intransitive) To halt the flow or movement of something.
(idiomatic, informal, intransitive) To fill up because of a backlog.
(obsolete) To run a printing press in reverse.