A person or, more symbolically, an institution will celebrate their birthday on the anniversary of the day they were born. People's birthdays are something that are celebrated in many different cultures. These celebrations may take the form of a party, a gift exchange, a card, or even a rite of passage.
Holidays such as Christmas, Mawlid, Buddha's Birthday, and Krishna Janmashtami are celebrated by many faiths throughout the world to commemorate the birth of their respective founders or other important religious leaders.
There is a difference between a person's birthdate and their birthday: the former is a specific day that, with the exception of February 29, occurs annually (for example, May 15), while the latter is the precise day that a person was born (e.g. June 11, 2004).