This has probably been asked a million times, but I am just curious. The inflight bells or notifications you hear (usually 1 or 2 dings) mean something, but I don't always know what. I've got the "above 10,000 ft. and you can turn on approved electronic devices" one figured out, but is there an explanation of these somewhere?

Are they used by the pilot/co-pilot to communicate to the rest of the crew? Or do they just mean, pick up the phone, we need to talk.

Again, just curious.

Thanks.