An aunt is a person who is the sister, half-sister or sister-in-law of a parent. Aunts are second-degree relatives and share 25% genetic overlap when they are the full sister of the parent. 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 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 or great-aunt is the sister or sister-in-law of a grandparent. The male equivalent of an aunt is an uncle, and the reciprocal relationship is that of a nephew or niece.
Thirteenth Aunt, Chinese given name Siu-kwan (少筠; "Siu-kwan", incorrectly translated in some subtitles as "Peony"), is a character created by Hong Kong director Tsui Hark for his 1991 martial arts film Once Upon a Time in China. Siu-kwan (Rosamund Kwan) is the Western-educated love interest of the protagonist, Chinese folk hero Wong Fei-hung.
Kwan reprised her role in four Once Upon a Time in China sequels films: Tsui's Once Upon a Time in China II (1992), Once Upon a Time in China III (1993), Once Upon a Time in China V (1994) and Sammo Hung's Once Upon a Time in China and America (1997). As a result of these films Siu-kwan became linked with the Wong Fei-hung legends, and was played by other actresses in later Wong Fei-hung media.
Wong Fei-hung respectfully calls Siu-kwan "Thirteenth Aunt", in accordance with Chinese traditions emphasizing generations and family status. In imperial China it was considered disrespectful to refer to Thirteenth Aunt as "Siu-kwan", despite her later insistence that Wong Fei-hung do so. Their romance is forbidden, since they are considered relatives; Siu-kwan's father is a blood brother of Wong's grandfather.