What is the meaning of backup?

noun

• An accumulation caused by clogging or a stoppage.
  • usage: "a traffic backup on the main street"; "he discovered a backup in the toilet"
• Someone who takes the place of another (as when things get dangerous or difficult. )
  • usage: "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins"
  • synonyms: stand-in, substitute, relief, reliever, backup man, fill-in
• A musical part (vocal or instrumental) that supports or provides background for other musical parts.
  • synonyms: accompaniment, musical accompaniment, support
• Computer science. ( a copy of a file or directory on a separate storage device)
  • usage: "he made a backup in case the original was accidentally damaged or erased"
  • synonyms: computer backup
• The act of providing approval and support.
  • usage: "his vigorous backing of the conservatives got him in trouble with progressives"
  • synonyms: backing, championship, patronage