A commemorative stamp from Azerbaijan, celebrating the 100th anniversary of the modern Olympic Games.

An anniversary is a day on which people remember or celebrate an event that happened on the same date in a past year. The most common example is a birthday, where the birth of a person is celebrated every year on the month and day of which they were born. The first anniversary of something is celebrated exactly one year after the initial event occurred. The word was first used for Catholic feasts to commemorate saints.