Pronunciation: (bak'up"),[key] —n. 1. a person or thing that supports or reinforces another.
2. a musician or singer or group of musicians or singers accompanying a soloist: a singer with a three-man backup that plays cello, bass, and guitar. 3. an overflow or accumulation due to stoppage, malfunctioning, etc.: a sewage backup; a backup of cars at the tollbooth. 4. a person, plan, device, etc., kept in reserve to serve as a substitute, if needed.
5. Computers. a. a copy or duplicate version, esp. of a file, program, or entire computer system, retained for use in the event that the original is in some way rendered unusable.
b. a procedure to follow in such an event.
6. Bowling.a ball that curves in a direction corresponding to the bowling hand of the bowler.
—adj. 1. (of a person, plan, device, etc.) held in reserve as a substitute if needed: a backup driver; a backup generator. 2. performing a secondary or supporting function: A drummer and guitarist are the singer's backup musicians.