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.
(..) That'd really help me out. It's on Samson, half block, silver Caprice. Just move it to the other side. They're street sweeping. There's spaces. Hang on to these. I have backups in my desk. And you have to jimmy that. - Jimmy what? - You have to jimmy the key. And the other doors don't unlock. (..)2006 The Pursuit of Happyness