A birthday is a day that comes once a year when a person celebrates the anniversary of his or her birth. Birthdays are celebrated in numerous cultures, often with a gift, party, or rite of passage. The celebration of a birthday usually is thought to mark how old a person is, traditionally stopping when death occurs and only stating that if still alive, they would have been (number of years) old. Some contemporary writers ignore this aspect, however, and keep counting the years since the date of birth of famous people, such as proclaiming that it is Shakespeare’s "four hundredth birthday" (although he died at the age of fifty-two) instead of noting that it is the four hundredth anniversary of his birth.
Many religions celebrate the birth of their founders with special holidays (e.g. Buddha’s birthday, Christmas).