In many countries, name days are just as important as birthdays, especially in countries with a religious background – Roman Catholicism, Orthodox religions, and some variations of Protestantism used to consider birthdays on the pagan side. The alternative was to celebrate the feast day of a particular saint that shared your name (back when nearly 100% of the population was named after some saint). This could be the saint whose feast day was the day you were born, or a patron saint of the family/city/country, or whatever profession your father worked. Since there was always a handy calendar of saint’s days, it was easy to remember what day was your name day.
In modern times, name days are still common in places like Eastern Europe (see previous comments on religious backgrounds), but also in Scandinavia, and name calendars have been updated to include more modern names. Name day fans say that name days are great because you don’t have to know a friend’s birthday in order to celebrate them – as long as you know their name, you can celebrate their name day. In Sweden, today is the name day for anyone named Estelle, meaning it’s Princess Estelle of Sweden’s very first name day. The Swedish royal court has released a few new pictures of Estelle (who is adorable as always) to mark the occasion. You can see them here and here, courtesy of Svensk Damtidning.
If you’re interested in finding out your own name day, you can check out calendar.name or do a search at HappyNameDay, which will give you name days in several countries – apparently in the USA, my name day is April 29th (also known as the Royal Cambridge Anniversary, which makes me a happy royal fangirl).