The Secret Rooms are a large network of rooms owned by Embless. Everybody owns one, and they can be accessed by going under someone's bed.
The Secret Rooms first appeared early in season five. At the time, they were simply rooms that everyone had. Most people put pictures of their crush in them.
On the last episode, it was discovered that Embless owned the network when he shut them down.
In season nine, Embless opened a Secret Room so him and Tyrell could hide from fangirls.
All the Secret Rooms are connected by a white hallway. The way to get into this hallway is unknown, but Embless is the only one who knows how to get in without using someone's secret room.
Secret Rooms only had one room, but you could extend them by purchasing extra rooms.