Typically used with a possessive determiner (my, his, her, their) or a noun in possessive form (e.g., Tariro's stepmother). In fairy tales the 'wicked stepmother' is a common character, but in modern usage the term is a neutral family descriptor.
常見錯誤
My step mother lives next door.
My stepmother lives next door.
'stepmother' is one word, not two.
My stepmother is my mother's new husband.
My stepmother is my father's new wife.
'stepmother' is the wife of one's father, not the spouse of one's mother.