Multiple players, in an MMO or muiltiplayer game, running together to accomplish a common task thats impossible to solo?

Just wondering I've never heard of something like that before. Was curious. Could be anything from like WoW and doing x boss as a guild or diablo 2 and completing hell difficulty from fresh characters. Diablo 2 does ladder resets pretty frequently and reset teams can often complete in less than 4 hours which is really impressive, but it would be a group effort, not one person.

Anyways just wondering.