Decennial

An anniversary is the date on which an event took place or an institution was founded.

Swedish celebrities including Miss Sweden Johanna Lind, Camilla Henemark, Alexandra Charles and Christina Schollin celebrate the 100th anniversary of the birth of Mae West at Berns in Stockholm in 1993

Memorial plaque presented by the National Capital Sesquicentennial Commission in Washington, D.C., in 1951

Most countries celebrate national anniversaries, typically called national days. These could be the date of independence of the nation or the adoption of a new constitution or form of government. There is no definite method for determining the date of establishment of an institution, and it is generally decided within the institution by convention. The important dates in a sitting monarch's reign may also be commemorated, an event often referred to as a "jubilee".

Names

• Birthdays are the most common type of anniversary, on which someone's birthdate is commemorated each year. The actual celebration is sometimes moved for practical reasons, as in the case of an official birthday or one falling on February 29.
• Wedding anniversaries are also often celebrated, on the same day of the year as the wedding occurred.
• Death anniversaries.

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). In ancient Rome, the [dies] Aquilae natalis was the "birthday of the eagle", the anniversary of the official founding of a legion.

Anniversaries of nations are usually marked by the number of years elapsed, expressed with Latin words or Roman numerals.

Numerical