noun /ˈbɜːθ.deɪ,ˈbɝθ.deɪ/
a) The anniversary of the day on which someone is born or something is created.
b) The date on which someone is born or something is created, more commonly called birthdate or date of birth.<!This is not an abbreviation of "birthday": abbreviation: DOB (date of birth.)
Wikipedia foundation.