A more thorough explanation:

Naturalis Possessio

Naturalis possessio is a Latin term that refers to the simple holding of a thing, often under a contract, with no intent of keeping it permanently. This type of possession exists when the possessor's holding of the object is limited by a recognition of another person's outstanding right. The holder may be a usufructuary, a bailee, or a servant.

• A person who borrows a book from a library has naturalis possessio of the book. They are holding the book temporarily and have no intention of keeping it permanently. The library retains the outstanding right to the book.
• A farmer who leases land from a landowner has naturalis possessio of the land. The farmer is holding the land temporarily and has no intention of keeping it permanently. The landowner retains the outstanding right to the land.

These examples illustrate naturalis possessio because in both cases, the holder is holding the object temporarily and recognizes that someone else has an outstanding right to it. The holder is not claiming ownership or intending to keep the object permanently.