Polite form of 誕生会, used when referring to someone else's birthday party or in formal contexts. The honorific お adds politeness.
See also: 誕生会
I was invited to my friend's birthday party next week.
Are the preparations for the birthday party ready yet?
Neutral form without the honorific prefix. Used for one's own party or in casual contexts.
More casual and Western-style term. Often used for informal gatherings.
Standard polite spelling with honorific prefix お.
Formal or literary spelling using the kanji 御 for the honorific prefix. Rare in everyday writing.
Compound of honorific prefix お + 誕生会 (birthday party). 誕生会 itself is from 誕生 (birth) + 会 (gathering).