"Ephemeral multiplayer" refers to the idea that you are briefly sharing the same digital space as one or more people, with minimal interaction.
I don't think there's a term for this, but it's probably in more than one game you've played. It can be positive or negative depending on how it got there. If there is a term for it, I'll change the title.
I was playing an online RPG in solo self-found mode and my experience with the game was enhanced by seeing other players in the world despite not actually interacting with them. I'm not sure why. I was playing it very much like a singleplayer game.
On the other hand, I've played MMORPGs that felt like this and it [editor's note: This was left unfinished]
The dork souls games and similar get into this a bit with sharing messages. I believe there's a daggerfall mod(or someone was working on one?) that had multiplayer inns, so you could go to an inn and interact with other players there, but nowhere else.
