What it means

1. 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”
2. noun an accumulation caused by clogging or a stoppage
   “a traffic backup on the main street”
3. noun the act of providing approval and support
   “his vigorous backing of the conservatives got him in trouble with progressives”
4. noun a musical part (vocal or instrumental) that supports or provides background for other musical parts
5. noun someone who takes the place of another (as when things get dangerous or difficult)
   “the star had a stand-in for dangerous scenes”