wēi​zǐ

son of a concubine

微子 wēi​zǐ
son of a concubine
(literary) a son not born to the legal wife or first wife
Weizi
Viscount of Wei (11th century BC), elder brother of the last Shang king and founder of the state of Song
adopted son
a son who has been taken into a family to be raised as their own