an accumulation caused by clogging or a stoppage; "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); "the star had a stand-in for dangerous scenes" "we need extra employees for summer fill-ins"

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

the act of providing approval and support; "his vigorous backing of the conservatives got him in trouble with progressives"