- (idiomatic, intransitive) To move backwards, especially for a vehicle to do so.
- That beeping sound indicates that the truck is backing up.
- (idiomatic, transitive) To move a vehicle backwards.
- Back up the car a little, you're blocking the driveway.
1898, Winston Churchill, chapter 5, The Celebrity:
- We expressed our readiness, and in ten minutes were in the station wagon, rolling rapidly down the long drive, for it was then after nine. […] As we reached the lodge we heard the whistle, and we backed up against one side of the platform as the train pulled up at the other.
- (idiomatic, intransitive) To undo one's actions.
- I couldn't see how to finish the project, so I backed up and tried it another way.
- (idiomatic, intransitive) To reconsider one's thoughts.
- This isn't working. Let's back up and think about it.
- (idiomatic, computing, transitive) To copy (data) as a security measure.
- Back up your documents folder before applying the update.
- (idiomatic, transitive) To provide support or the promise of support.
- You should be careful. This guy is backed up by the local gang.
- When he said I wasn't there, I told him I was, and my buddy backed me up.
- (idiomatic, intransitive, cricket) 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, cricket) 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, of a blockage) To halt the flow or movement of something.
- When I flushed the toilet, the plumbing backed up and burst.
To move backwards, especially for a vehicle to do so
To move a vehicle backwards
To copy as a security measure
For the non-striker to take a few steps down the pitch
For a fielder to position himself behind the wicket