Meaning of “backup” - Learner’s Dictionary

backup

noun uk us /ˈbækʌp/
SUPPORT [ C, U ]

B2 extra help, support, or equipment that is available if you need it:

Medical staff are on call to provide backup in case of an emergency.
COMPUTER [ C ]

B2 an extra copy of computer information:

to make a backup

(Definition of “backup” from the Cambridge Learner’s Dictionary © Cambridge University Press)