That is exactly it. An instance though is a copy of a specific map, say spacedock, where players will be automatically routed to as long as there is room. It can go up to 75 players atm I believe. When the instance is full another copy of that map is created and more players will be routed there.this is an open instance where players can interact doing different things. A prome example is the mythical Deferi invasion map where different objects appear interactible to players depending on their mission status. The majority of missions happens on closed instances that is specifically created for one player. You can join another players instance if you are teamed with him. On sone missions you have to be on the same mission steps or level to join him. Bur at all times you can interact with every player in the game at least per chat.