Each is just a different server. Think of it this way. There are two DUPLICATE worlds of the Aetherlight. Those are Roaring Springs and Lone Cog. You still have all of your personal stuff (inventory, wardrobe items, quests, etc.) regardless of which world/server you are in, but the number of players online in each is different. Because of that, usually one server has all of the filled-up engines while the other "world" rests in fog. Know what I mean? Hope this helps!