Definition of "Backup" :

noun: the act of providing approval and support

noun: (computer science) a copy of a file or directory on a separate storage device

"He made a backup in case the original was accidentally damaged or erased."

noun: a musical part (vocal or instrumental) that supports or provides background for other musical parts

noun: someone who takes the place of another (as when things get dangerous or difficult)

noun: an accumulation caused by clogging or a stoppage

"A traffic backup on the main street."