The policeman called for 'backup' [=called for other police to come and help him] because the suspect was carrying a gun.
There was a traffic 'backup' [=('Brit') 'tailback'] for miles on the road because of the accident.
His role on the team is to be a 'backup' to the regular quarterback.
(..) -It was okay? Okay, so you've got that one. Well, this is in bullet time. This is bullet time action. That was the backup plan. We had not completed making the rig that we needed to do the real shot. We wanted to make sure that we could do that scene ... ... if the bullet time (..)2001 The Matrix Revisited