What is the difference between out of order and out of service room?

There are two types of maintenance options available in general in most hotel management systems / PMS.

1)Out of Order (OOO) :-

Rooms kept under out of order are not sellable and these rooms are deducted from the hotels inventory. A room may be out-of-order for a variety of reasons, including the need of maintenance, refurbishing and extensive cleaning etc.

2)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.

Source : http://setupmyhotel.com/formats/front-office-codes-or-pms-codes/108-room-maintenance-code.html