A more thorough explanation:

Definition: Fideicommissary substitution is a legal arrangement where a person (the testator) leaves property to a beneficiary (the fiduciary), with the condition that the property will be passed on to another beneficiary (the fideicommissary) after the fiduciary's death.

For example, a wealthy man may leave his estate to his wife, with the condition that after her death, the estate will be passed on to their children. In this case, the wife is the fiduciary and the children are the fideicommissaries.

Another example is a person leaving a house to a friend, with the condition that after the friend's death, the house will be passed on to a charity. In this case, the friend is the fiduciary and the charity is the fideicommissary.

These examples illustrate how fideicommissary substitution works. The fiduciary is given temporary ownership of the property, but they are not allowed to dispose of it as they wish. Instead, they are obligated to pass it on to the fideicommissary after their death. This legal arrangement is often used in estate planning to ensure that property stays within a family or is used for a specific purpose.