The total quantity of material on open purchase, production or replenishment orders- total scheduled receipts.
"On order" is the term SRP uses to indicate that the correct amount of water is being delivered at the SRP gate.
A book that has been ordered from the publisher but has not yet been received. When it arrives, the library catalog will note that it is "in process" so you can request that it be rushed to you.
A term appearing on the Library catalogue - indicates that the item displayed has been ordered by the Library but not yet received.