backup

(băkˈŭpˌ)

1. a. A reserve or substitute.
   b. Computer Science A copy of a program or file that is stored separately from the original.
2. a. Support or backing.
   b. Music A background accompaniment, as for a performer.
3. An overflow or accumulation caused by clogging or by a stoppage: a backup in the sink; a backup of traffic at the drawbridge.