Former Surname, Maiden Name
noun
Your former surname is just that: your former surname! This is often your maiden name, as in the name you had before getting married.
きゅうせい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
いつもパスワードに母親の旧姓を使うんですよ。
I always use my mother’s maiden name as my password.