Polite form of 誕生日 (たんじょうび). Used when referring to someone else's birthday or in formal contexts. The honorific お adds respect.
Happy birthday (polite).
来週は母のお誕生日です。
Next week is my mother's birthday.
When is Mr. Tanaka's birthday?
Next month, my grandmother will turn eighty.
I gave my sister a birthday present.