Birthdays are the occasion to celebrate the day of someone's birth. Each year, children can't wait for this date, whereas adults are more sad than happy for it means that they got older. Most cultures celebrate birthdays as a tradition. On that occasion, a party is often organized (it may be a surprise) to get friends and family together. A birthday cake is also made or bought, which cake is very decorated, especially with as many candles as the age of the person. The latter is invited to make a wish before blowing out the candles.

Birthday songs are sang like the famous “Happy birthday to you” and gifts often offered. Those who could not make it may send a birthday card or a gift to tell their greetings for that special day. Parents often organize parties for their kid to get his friends and classmates together. They may make some invitation cards for the guests to say where the party is going to be and at what time. Guests may answer if they will come or not to make it the organization easier.

In some countries, the President or the King/Queen's birthday is celebrated nationally, as well as some historical “heroes” like Martin Luther King. Some events' anniversaries may also be celebrated like the anniversary of independence, which is also a holiday. Religious birthdays are also occasions for holidays, like the Christ birthday on December, 25, or Mahomet's one.

For the ones who were born on February 29, which only happens every four years, they celebrate the day before or the day after their day of birth, each year.