Witch House is a masquerade and dance event starting at October 28th at 6p.m. Wyrmrest Accord Time (PDT). The event takes place at Lake Jorune above Stonebreaker Hold in Terokkar Forest in Outland.
The event is neutral and cross-server. Be sure to have Cross RP and Elixir of Tongues handy to maximize your interactions with others during the event.
You can read more about this event on their forum post.