Orphan works are works that are still presumably under copyright, but the copyright owner cannot be found. In order to use these, you must demonstrate that you have made a reasonable effort to find and contact the copyright holder. Because this is not always possible, and at least very difficult, many of these works aren’t used.
If you have decided you need permission from a rights holder to use a copyrighted work, but can't locate any way to contact them, or never heard back from them after you contacted them, you might be dealing with an orphan work.
Unfortunately, a work's status as an orphan work does not allow you to treat the work any differently than any other work.
If you are in this situation, you must either,