A more thorough explanation:

Definition: Heres (heer-eez) is a Latin term used in Roman law to refer to a person who succeeds to the rights and liabilities of a deceased person, i.e., an heir.

The heres was responsible for both the rights and debts of the decedent, which combined the roles of a modern executor and an heir at law. The institution of the heres was a crucial characteristic of a testament, and if this was not done, the instrument was called a codicillus.

Examples:

• Heres ex testamento: This refers to an heir appointed by will, also known as a testamentary heir. For instance, if a person writes a will and names their child as the heres, then the child becomes the heres ex testamento.
• Heres natus: This refers to an heir by reason of birth, i.e., an heir at law or by intestacy. For example, if a person dies without a will, their child becomes the heres natus.
• Heres extraneus: This refers to an external heir, i.e., one who had not been subject to the testator's power (potestas) and hence not bound to accept the inheritance. For instance, if a person writes a will and names their friend as the heres, then the friend becomes the heres extraneus.

These examples illustrate how the term heres is used in Roman law to refer to different types of heirs, depending on how they inherit the deceased person's estate.