1
general::
Phrase(s): on order
ordered with delivery expected. • Your car is on order. It’ll be here in a few weeks. • I don’t have the part in stock, but it’s on order.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Requested but not yet delivered, as in Our new sofa is on order. This term is always used for goods of some kind, the noun order having been used in the sense of "a commission for goods" since the early 1800s.
American Heritage Idioms