A more thorough explanation:

An Indian child is a person who is under the age of 18, unmarried, and either a member of an Indian tribe or eligible for membership in an Indian tribe and the biological child of a member of an Indian tribe.

The Indian Child Welfare Act (ICWA) is a federal law that governs child-custody proceedings involving a child of American Indian descent. The Act aims to protect the best interests of Indian children, promote the stability and security of Indian tribes and families, and counteract the disproportionate foster-care placement and adoption of Indian children by non-Indians.

The ICWA provides minimum federal standards for removing Indian children from their families and placing them in foster or adoptive homes that reflect the values of the Indian culture. In a custody dispute involving an Indian child who resides in or is domiciled within an Indian reservation, the tribe and its tribal courts have exclusive jurisdiction. In a custody dispute involving an Indian child who lives off a reservation, any state court should usually defer and transfer the case to the tribal court unless a party demonstrates good cause to the contrary.

An example of an Indian child is a 16-year-old girl who is a member of the Navajo Nation and lives on the reservation with her family. If there were a custody dispute involving her, the Navajo Nation and its tribal courts would have exclusive jurisdiction over the case.

Another example is a 10-year-old boy who is eligible for membership in the Cherokee Nation and lives off the reservation with his non-Indian foster parents. If there were a custody dispute involving him, any state court should usually defer and transfer the case to the Cherokee Nation tribal court unless a party demonstrates good cause to the contrary.

These examples illustrate how the Indian Child Welfare Act applies to children who are members of or eligible for membership in Indian tribes and how the Act aims to protect their best interests and promote the stability and security of Indian tribes and families.