Noun
1. an accumulation caused by clogging or a stoppage;
"a traffic backup on the main street""he discovered a backup in the toilet"2. 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"3. a subordinate musical part; provides background for more important parts
4. (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"5. the act of providing approval and support;
"his vigorous backing of the conservatives got him in trouble with progressives"