What do you consider to be the difference between an MMO and a live-service RPG?

I’ve been thinking more and more about the question — “Is Diablo 4 an MMO?” — since I currently play World of Warcraft, am pretty heavily invested in Diablo 3, was into Diablo Immortal for a couple of months there, and was just utterly charmed by the open beta for Diablo 4. In particular, the way D4 mixes things I’ve seen in each of the other games I’ve mentioned makes it difficult sometimes for me to really confidently say that Diablo 4 isn’t an MMO.

I mean, I get that it’s a game I can play entirely in single-player for the most part, with closed off play in Dungeons and Cellars plus upcoming Seasonal play after it launches. But it also has always online play; I see other players on their characters every time I head back to town and out in the world — I even often found myself stopping to help them in world events and against giant monsters they were fighting.

This is one of those times where I’m not even sure if it would be helpful to define Diablo 4 in that way or in those terms. I’ve seen people call it a live service game, but a lot of the live service games I’ve seen look a lot like MMOs, and the line feels like it gets blurrier and blurrier with even World of Warcraft adding the Trading Post with its monthly rewards.

I mean, an MMORPG where I literally never have to group and can just play the entire game solo isn’t exactly a new thing. Diablo 4 has clans (as did Diablo 3) like Diablo Immortal, but it also has couch co-op play and console/PC cross platform play. It’s not something most MMOs do.

Does it matter? Honestly, I don’t know. It’s a question we’ve covered in the past, but with actually having gotten to play in the open beta, I’m honestly asking it again. Because Diablo 4 does basically everything I wanted Diablo Immortal to do, and improves on the things it did that I liked. Character customization (there could be more, but it’s still good), potential group play, a much better story — indeed, based on the first 20 or so levels, maybe the best story Diablo has ever had — so maybe I should just shut up and be grateful it’s so good. But what do y’all think?