What is Bona Vacantia?

Legal Definition
Bona vacantia (Latin for "ownerless goods") is a legal concept associated with property that has no owner. It exists in various jurisdictions, with consequently varying application, but with origins mostly in English law.
-- Wikipedia
Legal Definition
Vacant, unclaimed, or stray goods. Those things in which nobody claims a property, and which belong to the crown, by virtue of its prerogative. 1 Bl. Comm. 298.
-- Black's Law Dictionary
Legal Definition
Goods to which no one claims a property, as, shipwrecks, treasure trove, &c.; vacant goods.
-- Bouviers Law Dictionary
Legal Definition
Civil law. Goods without an owner. Such goods escheat.
-- Bouviers Law Dictionary
Legal Definition
Unclaimed or abandoned goods.
-- Ballentine's Law Dictionary