What does birthday mean?
A birthday is the anniversary of the date on which a person was born, observed each year on that calendar date. The word also denotes the actual day of birth when discussed historically or biologically. Birthdays are among the most widely celebrated personal occasions across cultures, typically marked with greetings, gifts, cakes, candles, and gatherings of family and friends, and milestone birthdays — such as an eighteenth or twenty-first — often carry particular social weight as markers of adulthood or new legal rights. The noun functions neutrally in both formal and informal registers: it appears in legal documents ('date of birth' contexts) as readily as in casual conversation. Fixed expressions like 'happy birthday', 'birthday party', 'birthday cake', and 'birthday present' are firmly established in everyday English. Although now universal, the custom of celebrating ordinary people's birthdays annually is relatively modern, having spread broadly only from the nineteenth century onward.
The anniversary of the date on which a person was born.
"All her friends gathered for her birthday."
Usually takes a possessive or determiner: 'my birthday', 'her birthday'.
The day on which a person was born.
"Records show his birthday as 4 July 1890."
Standard plural; commonly used when referring to multiple people's anniversaries or recurring celebrations over time.
"They have shared many birthdays together since they met."
For most of history, ordinary people didn't celebrate their birthdays at all — the annual birthday party is largely a modern invention, popularised by the Victorian middle classes.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of birthday
Birthday is a compound of 'birth' (from Old English 'gebyrd', related to the verb 'to bear') and 'day' (Old English 'dæg'). The compound has ancient roots: it translates Latin 'dies natalis', used for the anniversary of birth and, in imperial Rome, of notable events or figures. The English compound is attested by late antiquity in religious usage and became common in modern English for personal anniversaries. Its components are thoroughly Germanic, making it a native formation rather than a borrowing.
Related word forms
How birthday is actually used
A common, neutral noun used in both formal and informal contexts. 'Happy birthday' is the standard fixed greeting. In British English, ordinal phrasing such as 'her twenty-first birthday' is standard for milestone celebrations; American English often says 'twenty-first birthday' identically, so no major regional difference applies to the word itself.
Easily confused with birthday
'Birthdate' refers to the calendar date of one's birth as recorded information, whereas 'birthday' refers to the anniversary of that date celebrated each year.