/ ˈbækʌp; NAmE / noun [ U , C ]
1.
extra help or support that you can get if necessary :
The police had backup from the army.
We can use him as a backup if one of the other players drops out.
a backup power supply
2.
( computing ) a copy of a file, etc. that can be used if the original is lost or damaged :
Always make a backup of your work.
a backup copy
—see also back up