Res nullius

Res nullius is a fancy way of saying "nobody's thing." When something is res nullius, it belongs to nobody and anyone is free to pick it up and keep it or use it as they wish.

Think about a leaf that has fallen off a tree. It doesn't belong to anyone, so you can pick it up, examine it, take it home, or throw it away. Nobody will come after you and say, "Hey! That's my leaf! Give it back!" because it's res nullius.

Likewise, imagine a toy truck that you find in a public park. If nobody is around claiming it, you can pick it up and play with it because it's res nullius. But if another kid comes up and says "That's mine!", you need to give it back.

Res nullius means you are allowed to use or keep something that does not belong to anyone yet, but once someone claims that thing, it becomes their property and you can't take it away from them.