Niece and nephew

In the lineal kinship system used in the English-speaking world, a niece or nephew is a child of an individual's sibling or sibling-in-law. A niece is female and a nephew is male, and they would call their parents' siblings aunt or uncle. The gender-neutral term nibling has been used in place of the common terms, especially in specialist literature.

As aunt/uncle and niece/nephew are separated by one generation, they are an example of a second-degree relationship. Unless related by marriage, they are 25% or more related by blood if the aunt/uncle is a full sibling of one of the parents, or 12.5% if they are a half-sibling. Provided by Wikipedia