The phrase "lost treasure" refers to valuable items or wealth that has been misplaced, hidden, or taken and cannot be found or claimed by anyone else. Full definition
I'm always telling you stories about me finding lost treasures in my closet like this ruffle skirt, for example. (beeswonderland.com)
Meanwhile, the real thief uses the pop - up book to hunt for a rumored lost treasure. (artsbham.com)
If the department shut down, we might also lose a treasure trove of data gathered from across the country on educational outcomes and the demographics of student and teacher populations. (thinkprogress.org)