bona vacantia
noun
Definitions
The principle that there is no unowned property, and that if there is no other owner then property vests in the Crown.
Example: "The company asked also for an express vesting order concerning the land, which had legally gone to the Crown as bona vacantia" http//books.google.co.uk/books?id=WvY3AAAAIAAJ&pg=PA814&dq=bona+vacantia