I know what the word means, but I’m unsure how to use it in a sentence. In my native language, Danish,“backorder” translates to “Restordre” and when something is unavailable, we say it’s"i Restordre",which translates directly into English as “in backorder”, but I’m not sure that’s correct English. Do English people say that or just “backordered” or something else?
“Backordered” or “On backorder” are the normal usages as an adjective.
But “In backorder” would also be perfectly understandable.