Anniversary
An anniversary is a day that commemorates or celebrates a past event that occurred on the same date of the year as the initial event. For example, the first event is the initial occurrence or, if planned, the inaugural of the event. One year later would be the first anniversary of that event. The word was first used for Catholic feasts to commemorate saints.
Anniversary names
Birthdays (v.) are the most common type of anniversary, where the birth date of a person is commemorated annually. The actual celebration is sometimes moved for practical reasons, as in the case of an official birthday.
Wedding anniversaries are also often celebrated on the same day of the year as the wedding occurred.
Death anniversary.
The Latin phrase dies natalis (literally "birth day") has become a common term, adopted in many languages, especially in intellectual and institutional circles, for the anniversary of the founding ("legal or statutory birth") of an institution, such as an alma mater (college or other school). Even in ancient Rome, we know of the [dies] Aquilae natalis ("birthday of the eagle", anniversary of the official founding of a legion).