noun (n)

• an accumulation caused by clogging or a stoppage(noun.process)

  Example:
  A traffic backup on the main street.
  He discovered a backup in the toilet.
  

  source: wordnet30
• someone who takes the place of another (as when things get dangerous or difficult)(noun.person)

  Synonym:
  backup man, fill-in, relief, reliever, stand-in, substitute
  

  source: wordnet30
• a musical part (vocal or instrumental) that supports or provides background for other musical parts(noun.communication)

  Synonym:
  accompaniment, musical accompaniment, support
  

  source: wordnet30
• (computer science) a copy of a file or directory on a separate storage device(noun.artifact)

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

  Synonym:
  computer backup
  

  source: wordnet30
• the act of providing approval and support(noun.act)

  Synonym:
  backing, championship, patronage
  

  source: wordnet30