also back-up
(~s)
1.
Backup consists of extra equipment, resources, or people that you can get help or support from if necessary.
There is no emergency back-up immediately available...
Alternative treatments can provide a useful back-up to conventional treatment.
N-VAR
2.
If you have something such as a second piece of equipment or set of plans as ~, you have arranged for them to be available for use in case the first one does not work.
Every part of the system has a ~...
Computer users should make regular back-up copies of their work.
N-VAR