I was going to use the word “broadcast” too, but I was wary because I could not find any articles that used that word in connection with MIDI (it’s predictable but still funny how the LLMs go quiet or change the subject in such situations 
). But yes, I think it’s an appropriate term or at least analogy.
Yes, that’s how MIDI works. When a key is pressed on a MIDI keyboard controller, the keyboard sends the data over the specified channel and that’s it. It’s job has been done. Maybe the message will be heard by a computer and a piano module or maybe nothing else is plugged in, but none of that is of concern to the keyboard, which has done its job.
Most MIDI hardware these days will carry MIDI over USB connections, but the protocol is the same as when carried over those old DIN connections that you might still see on the back of some MIDI keyboards. One is for MIDI in and one is for MIDI out[1] and that reminds us that MIDI 1.0 is a unidirectional protocol. If we want to hear back from the computer or sound module, we need a separate line for that.
Checks... Yes, as I seemed to remember, MIDI 2.0 offers bidirectional communication but that’s a whole new can of worms. As the MIDI Association says: “MIDI 2.0 may seem really complicated. Yes, it actually is more complicated…”
Yes, you may also see “MIDI thru” but that is just repeating the incoming MIDI. ↩︎