verb To move backwards, especially for a vehicle to do so.
That beeping sound indicates that the truck is backing up.
verb To move a vehicle backwards.
Back up the car a little, you're blocking the driveway.
verb To undo one's actions.
I couldn't see how to finish the project, so I backed up and tried it another way.
verb To reconsider one's thoughts.
This isn't working. Let's back up and think about it.
verb To copy (data) so that it can be restored if the main copy is lost.
Back up your documents folder before applying the update.
verb To provide support or the promise of support to.
You should be careful. This guy is backed up by the local gang.
verb 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.
verb 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.