An honorific/respectful way to refer to someone's mother (or one's own mother in polite contexts).
お母様は本日ご在宅でしょうか。面会の予約をしたいのですが。
Is your mother at home today? I'd like to make an appointment to see her.
お母様にどうぞよろしくお伝えください。
Please give my regards to your mother.
結婚式で新婦はお母様に花束を渡した。
At the wedding, the bride gave a bouquet to her mother.