The day halfway in between two consecutive birthdays.

plural of birthday boy

A woman or girl whose birthday it is.

A man or boy whose birthday it is.

A greeting card given to someone to celebrate his or her birthday.

(idiomatic, often humorous) Nakedness, unclothed skin; an exposure of a human's natural anatomy without clothing. / Used other than figuratively or idiomatically: see birthday, suit.

A cake, often iced and decorated, made to celebrate a person's birthday.

(cryptography) A covert method of decryption exploiting the so-called birthday paradox.

(probability theory) The mathematics problem that concerns the probability there exist two people in a random group who share a birthday.

(statistics) A statistical phenomenon where an individual's likelihood of death appears to increase on or close to their birthday, variously attributed to alcohol consumption, psychological stress, increased suicide risk, and other factors.