Out-of-order: The room cannot be assigned to a guest. A room may be out-of-order for a variety of reasons including the need for maintenance, refurbishing, and extensive cleaning.
Out of Service (OOS ): Rooms kept under out of service are not deducted from the hotel inventory. This is a temporary blocking and reasons may be bulb fuse, T V remote not working, Kettle not working etc. These rooms are not assigned to the guest once these small maintenance issues are fixed.