Are they like raids or something?

I think they are, not too sure myself.

From various descriptions I feel they are more like 50+ overworld content where all 3 alliances can PvE together, with public dungeons and 12men dungeons. These lasts ones are more aimed towards the raid crowd.

@Damanta, I think I saw one of those on a YouTube video and those look awesome! So many enemies just waiting to be killed!