A more thorough explanation:

Definition: Jus ad rem is a legal term that means "right to a thing." It refers to a right in specific property that arises from another person's duty and is only valid against that person. It is an incomplete or inchoate right to a thing. This is different from jus in re, which is a complete or perfect right to a thing.

One example of jus ad rem is a mechanic's lien. If a mechanic repairs a car and the owner fails to pay for the repairs, the mechanic may have a right to the car as security for the debt. This right is only valid against the owner of the car and is incomplete until the debt is paid.

Another example is a mortgage. If a borrower fails to make payments on a mortgage, the lender may have a right to foreclose on the property. This right is only valid against the borrower and is incomplete until the foreclosure process is complete.

These examples illustrate the concept of jus ad rem because they show how a right to specific property can arise from another person's duty and be valid only against that person. The right is incomplete until certain conditions are met, such as payment of a debt or completion of a foreclosure process.