noun
happy event; cause for celebration; congratulations
Polite noun used to refer to a joyous occasion or to express congratulations. Often appears in formal greetings or announcements.
See also: 慶事 (けいじ)
ご結婚のお喜びを申し上げます。
Congratulations on your marriage.
新年のお喜びを申し上げます。
Happy New Year (formal congratulations).
慶事 is a more formal, written term for a happy event, while お喜び is a polite, often spoken expression of congratulations.
Polite prefix お + nominalized form of 喜ぶ (to rejoice). The kanji 慶 is used in formal contexts for celebratory events.