A backorder is an automated service that attempts to register, or “catch” a domain name at the end of its full lifecycle when it’s made available for registration again after expiring.
When a domain state shows "Backorder" it means that it has already been registered. If you choose to backorder the domain, what happens is that when the domain drops our system will attempt to catch it for you.
Please note that if the owner chooses to renew it, the backorder will stay in place because the domain did not reach the drop period.
A domain may take from 35 to 75 days after expiration in order to enter the drop period.