> I sometimes wonder if everyone is talking about the same thing, but using different language to describe it

As someone who can hear music "on demand" in my head I can say that's not the case. I can hear the music with instruments and the original singer's voice. It's not as clear as listening to actual music, and in some cases it may be incomplete if I havent' listened to the song for a while, but it's definitely a playback.

As an example, right now I am thinking of The Trooper by Iron Maiden, and I can hear the drums, base, guitars and the lead singer's own voice. I can also separate the different instruments if I want to listen to just the guitar or the singer's voice because I know the song well. I can also change the lyrics or the guitar solo if I want.

It's the same as imagining an image. It is not a perfect reproduction of a "photo" that pops up in my mind, but it is still an image with colours, shapes and faces.

I understand where you are coming from, because you don't have the necessary context. When I read about people who "see" music in colours or smells, or even simple colour blindness, it is hard to imagine. But I still accept that it exists