Definition
Said when a difficult situation ends abruptly, usually just before someone has to do or say something they would rather avoid.
I was about to answer that tricky question when the phone rang; saved by the bell!
The meeting was about to start, and I wasn't prepared with my report, but the manager postponed it, so I was saved by the bell.
The fire alarm went off just before the boss was about to ask me about my progress, it was a total 'saved by the bell' moment.