To wait in expectation of some event; to make ready.
Please stand by for more instructions.
To remain loyal or faithful to.
Even though money is scarce sometimes, Ann stands by her decision to be a full-time mother.
To support; to continue to support despite things being bad.
They stood by us all along and it's awesome to see them out here to support us today.
To do nothing. To be inactive in a situation.
I can't simply stand by and watch you ruin your life.
To be ready to provide assistance if required.
The tug stood by in case it was needed.
A state of readiness without immediate involvement; remaining in preparation for (a sudden or unforeseen event or situation).
The troops were on standby in case of an attack.
Sleep mode
(travel) Waiting at the airport in the hope of getting a seat on a flight that is already booked out.
Something that is standard, well-tested, or frequently used.
That recipe is an old standby, and she keeps the ingredients around in case of unexpected guests.