It looks like you're new here. If you want to get involved, click one of these buttons!
We should not be that narrow minded and limit massive multiplayer interaction to pve grouping, or pvp battles.
There are lots of other ways players can interact and impact each other.
One very prominent example is trading. If you can trade with millions of others in a AH, or any other trading mechanism, how is that not massive, not multiplayer, and not interactive?
Another example is just inspection (for seeing items, for status, for whatever reasons). If you can LOOK AT thousands of other players and what they wear, how is that not massive? How is that not multiplayer? In fact, that is a big part of the now defunct SIMS online.
And a MMO does not need massively multiplayer in all aspect of its gameplay. What if it is massively multiplayer in trading, but support a lot of solo-ing in combat? In fact, that is how a lot of current MMO operates. That is the point. Players cannot get a solo-combat experience, combined with a massively trading experience, in a single player game, can they?