Meaning of “stand by” - Learner’s Dictionary

stand by

phrasal verb with stand uk us /stænd/ verb (past tense and past participle stood)
BE READY

to be ready to do something or to help:

Doctors were standing by to treat the injured passengers.
DO NOTHING

to do nothing to prevent something unpleasant from happening:

We can't stand by while millions of people starve.

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