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.”

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.