Here's a breakdown:

* Cablegram: A message sent over a submarine telegraph cable.

* Telegraph: A system for transmitting messages over long distances using electrical signals.

The telegraph machine itself was comprised of several parts:

* Key: Used to send Morse code signals.

* Sounder: Used to receive Morse code signals as audible clicks.

* Receiver: A device that converted electrical signals into visible symbols (usually on a strip of paper).

While submarine cables were instrumental in the development of cablegrams, the underlying technology was still the telegraph.