A more thorough explanation:

Definition: A niece is the daughter of a person's brother or sister. It can also refer to the daughter of a person's brother-in-law or sister-in-law. In some cases, a grandniece may also be referred to as a niece. A half-niece is the daughter of one's half-brother or half-sister.

• My sister's daughter is my niece.
• My brother-in-law's daughter is also my niece.
• My cousin's daughter is my grandniece, but I still refer to her as my niece.
• My half-sister's daughter is my half-niece.

These examples illustrate how a niece can be related to a person through different family members. It also shows how the term can be extended to include grandnieces and half-nieces.