A polite term for someone's birthday — used often in greetings and celebratory contexts.
お誕生日おめでとうございます！素敵な一年になりますように。
Happy birthday! I hope you have a wonderful year.
来週は母のお誕生日なのでプレゼントを用意した。
Next week is my mother's birthday, so I prepared a present.
会社では同僚のお誕生日にみんなでケーキを買うことが多い。
At the office, it's common for everyone to buy a cake for a colleague's birthday.