definition of
backup

[1] #1 backup n. an accumulation caused by clogging or a stoppage; "a traffic backup on the main street"; "he discovered a backup in the toilet". wn

[2] #2 backup n. [stand-in, substitute, relief, reliever, backup man, fill-in] someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins". wn

[3] #3 backup n. [accompaniment, musical accompaniment, support] a musical part (vocal or instrumental) that supports or provides background for other musical parts. wn

[4] #4 backup n. [computer backup] (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". wn

[5] #5 backup n. [backing, championship, patronage] the act of providing approval and support; "his vigorous backing of the conservatives got him in trouble with progressives". wn