B/U

Noun

backup (countable and uncountable, plural backups)

1. A reserve or substitute.
   • If the goalkeeper is injured, we have a backup.

   Synonyms:

   stand-in, substitute

2. A copy of a file or record, stored separately from the original, that can be used to recover the original if it is damaged or destroyed.
   • After the power failure, we had to restore the database from backup.
3. An accumulation of material caused by a (partial) obstruction or (complete) blockage of the flow or movement of the material, or an accumulation of material that causes an overflow due to the flow being greater than the maximum possible flow.
   • The accident caused a mile-long backup on the highway.

   Synonyms:

   tailback, line

4. (uncountable) Reinforcements.
   • He's got a gun! You'd better send for backup.
5. (broadly, uncountable) Any support or extra help.
   • Shaman: My patience is tested, but Uvenk invokes correctly. Grunt, who is your krantt? Your allies willing to kill and die on your behalf?
     Shepard: How is a candidate tested if he brings backup on his Rite of Passage?
     Shaman: Not every krogan can be the strongest warrior, but each must inspire his...2010, BioWare, Mass Effect 2 (Science Fiction), Redwood City: Electronic Arts, →OCLC, PC, scene: Tuchanka
6. (uncountable) Accompaniment.
   • Debbie Ahn, on piano, provided some mesmerizing back-up and many fiery, on-target solos.1984 April 21, Pam Gordon, “'There's Always Cost': Ferron's Boston Concert”, in Gay Community News, page 17

See all 10 meanings of backup