A more thorough explanation:

Definition: Incest is when people who are closely related have sexual contact or get married. This includes brothers and sisters, parents and children, grandparents and grandchildren, or aunts or uncles with nephews or nieces. It is against the law in all states, even if both people agree to it.

Examples:

• A father having sexual contact with his daughter
• A brother and sister getting married
• An uncle having sexual contact with his niece

These examples show how incest involves sexual contact or marriage between close relatives, which is not allowed by law.