Res nullius, is a Latin-based legal term that refers to a property or object that has no owner or has been abandoned. The term is derived from Roman law and, when translated, literally means "nobody’s property." There are a variety of objects that can be claimed as res nullius and are considered ownerless property, meaning they are free to be owned.
In this definition, the object, or ‘res’, must be something a person can claim to own. While the law covers animals and land, the object in question cannot be a person, though its original meaning covered slaves as property rather than as people. As stated by law, if the owner of an object abandons or gives up his property, then it is automatically deemed res nullius. Traditionally, the abandoned property can then be owned by any person and the person who first takes possession of said property is deemed its rightful owner. Res nullius does not apply to any object or property that has been stolen or illegally acquired, only to property that has no owner or has been abandoned.
A property or possession that has been abandoned by its owner is equally as res nullius as something that never had an owner in the first place. This principle means res nullius is also often used as a term to describe a situation in which a nation may stake a claim to unmarked territory. The territory is res nullius and has no owner, so the nation staking claim would gain control over the territory once one of its citizens steps foot on the uncharted land. In these specific situations, when a nation actually claims an unmarked territory is formally referred to as terra nullius.
That same guiding principle also applies to certain wild animals. Wildlife laws have been established that say certain animals in the wild are res nullius and can be owned. They are not abandoned, but the animals in the wild have never been owned, so the first person to capture or kill the animals would be deemed the proper owner. For example, a wild bird in a bush is res nullius, but a wild bird in someone’s hand is now that person's possession.
Finding or acquiring something that is res nullius can also be a way to gain ownership. That works if the thing is truly and completely lost or abandoned and is later found by another person. Therefore, if long-lost treasures or artifacts have been deemed permanently lost and are later recovered by treasure hunters or beachcombers, they would fall under res nullius and become the property of the first person to find them.