A niece (the daughter of one's brother or sister); an informal, familiar term commonly used in speech.
日曜日は姪っ子を遊園地に連れて行った。
On Sunday I took my niece to an amusement park.
姪っ子が来年から中学生になります。
My niece will start junior high school next year.
写真を見せたら、姪っ子がかわいいとみんなが言った。
When I showed the photo, everyone said my niece was cute.