1.Anything kept in reserve to serve as a substitute in case of failure or unavailability of the normal or primary object; used for devices, plans, people, etc. Also used attributively; as, there was no backup for the electrical supply; a backup motor; a backup generator.
2.(Music) A musician or group of musicians accompanying a soloist, whether vocalists or instrumentalists.
3.A person or group of persons serving as reinforcement for another or others; as, the policeman called for backup when he was fired on.
4.An accumulation, overflow, or reverse flow (in traffic or a liquid flow system) caused by a stoppage or other malfunction.
5.(Computers) A copy of a program or data from a computer onto a data-storage medium, usually one that may be removed to safe storage at a distance from the computer; it is used to preserve data for use in the contingency that the original data on the computer may be lost or become unusable. A backup that is removed from the building housing the computer system (to provide protection against loss of data in a disastrous event such as a fire) is called off-site backup. Also used attributively; as, backup copy.
6.(Computers) The act or process of creating a backup (5); as, they performed a full system backup every weekend.
