A centennial is a 100th anniversary, the celebration of something that happened exactly one hundred years ago. When a town marks its centennial, it's commemorating the day it was founded a century earlier. Schools celebrate centennials. So do organizations, buildings, and important historical events.

You might see centennial celebrations with special ceremonies, historical exhibits, or commemorative coins. In 1876, America celebrated its centennial with a massive World's Fair in Philadelphia, marking 100 years since the Declaration of Independence. In 1976, the country celebrated its bicentennial (200th anniversary).

Centennials matter because they give us a chance to look back at how much has changed over a full human lifetime. Someone born in your town's founding year would have lived their entire life by the time the centennial arrived. That's why these celebrations often include stories from elders, old photographs, and reflections on progress.

As an adjective, centennial describes something connected to a 100th anniversary, like a centennial parade or a centennial museum exhibit.

Related words follow the same pattern: a bicentennial marks 200 years, a sesquicentennial celebrates 150 years, and a semicentennial commemorates 50 years (though people usually just say “50th anniversary” for that one).