Jus ad rem is a fancy way of talking about the right to something that belongs to you. It's like saying that you have a special way of getting what is yours if someone tries to take it away from you. You have a special power to protect what is yours and make sure nobody else takes it from you.
Imagine you have a toy that is yours, and you love playing with it. But one day, another kid comes along and tries to take it away from you. This isn't fair, because it's your toy and you have the right to play with it. Jus ad rem is like having an invisible shield around your toy that keeps it safe from others who try to take it away. You can use it to protect your toy and make sure nobody takes it away from you without your permission.
Jus ad rem is really important for grown-ups too, especially when it comes to money or property. It means that you have the right to keep what is yours, and nobody can take it away from you without a good reason. So, if someone tries to take your house or your car, you can use jus ad rem to protect it and make sure it stays yours.
Overall, jus ad rem is just a fancy way of saying that you have a special power to protect things that belong to you, like toys or even important grown-up stuff like property and money.