So basically, it's an mmo I can play as a single player game by using Solo mode. Got it.
But you
can’t Play ED like a single player game. That’s the point.
For example, recently I was in the middle of lifting off of a planet in Space Engineers, en route to a space station, when real life interrupted. I saved my game, dealt with the interruption, loaded the game, and resumed
exactly where I left off. Not that long ago, I was in the middle of a stealth mission in another single player game when I realized it was getting late. I saved my game in the middle of sneaking up on an enemy, and left it there. Didn’t get back to it for three days. When I did, I resumed playing
exactly where I left off.
If I were in the middle of Orbital Cruise on approach to a space station in ED, I wouldn’t be able to log out in to middle, and expect to drop back into the
exact same conditions I left them in. I’d be in normal space, and that station would likely be on the far side of the world. If I were to attempt a stealth mission in ED, I wouldn’t be able to log out, and return three days later to resume the mission, already in progress. If I don’t get kicked out of the settlement
completely, the guards would be in different places, the mission would’ve failed, and the settlement could be in a
completely different state from when I last left it.
As for the definition of “massively multiplayer”…
Single Player < Multi-Player (LAN) <= Multi-Player (WAN) <= MUDs* <= Massively Multi-Player
It’s a relative term, not a quantitative one. It simply means that there are more players in the game than the typical MUD*, private hobby server, or other small-scale multi-player games.