"stand by” means “to remain tuned into a station until it starts sending messages. “Please stand by” for an important announcement.
“Stand by” also means “to stand near, look on without interfering.” He stood by watching the fight.
Another meaning of “stand by” is “to remain loyal or faithful.” He stood by me in the crisis. They stood by me through all my difficulties. She did not let us down. She stood by her promise.