english
1
general::
An item not currently in stock but to be sold or delivered when it becomes available, as in We don't have the shoes in white, but we can make them a back order. The verb back-order means "to obtain such an item," as in The furniture store is going to back-order the sofa for us.
American Heritage Idioms
2
general::
Phrase(s): back-order something [for a merchant] to order something that is not in stock and make delivery to the customer when the goods become available. • The store didn’t have the replacement part for my vacuum cleaner, so the manager back-ordered it for me. • The shop had to back-order some of the items on my list.
McGrawhill's American Idioms And Phrasal Verbs