The main difference between Niece and Aunt is that the Niece is a child of one’s sibling or half-sibling and Aunt is a kin; sister of a parent.
In the language of kinship, a nephew is a son of a person’s sibling, and a niece is a daughter of a person’s sibling. Conversely, that person is the aunt or uncle of their niece or nephew. The relationship of aunt/uncle to niece/nephew is an example of second-degree relatives, meaning that their coefficient of relationship is 25%.
The terms are also used colloquially for sons and daughters of siblings-in-law, even though there is no blood relationship.
An aunt is a person who is the sister, half-sister, step-sister, or sister-in-law of a parent, or the wife of one’s uncle or aunt, but can also be an affectionate title for an older nurturing woman. Aunts are second-degree relatives and share 25% genetic overlap when they are the full sister of one of the biological parents. Known alternate terms include Auntie or Aunty. A half-aunt is a half-sister of one’s parent and is a third-degree relative with 12.5% genetic overlap. If the aunt is a step-sister or sister-in-law, direct genetic overlap will typically be 0%, as this person entered the family through marriage and typically is not a blood relative.
A grand-aunt (sometimes written as grand aunt, grandaunt, or great-aunt) is the sister, half- or step-sister, or sister-in-law of a grandparent, or the wife of one’s grand-uncle or grand-aunt. The male equivalent of an aunt is an uncle, and the reciprocal relationship is that of a nephew or niece.
A daughter of one’s sibling, brother-in-law, or sister-in-law; either the daughter of one’s brother (“fraternal niece”), or of one’s sister (“sororal niece”).
“My niece just celebrated her 15th birthday.”
The sister or sister-in-law of one’s parent.
A woman of an older generation than oneself, especially a friend of one’s parents, by means of fictive kin.
Any elderly woman.
A procuress or bawd.