What term describes the 250th anniversary being celebrated by America250?

The term describing America250's 250th anniversary celebration is semiquincentennial.

The word combines Latin-derived number elements: semi means half, quin means five, and centennial refers to a period of 100 years. Half of five centuries is 250 years, giving semiquincentennial its meaning. The United States Semiquincentennial is therefore the formal historical term for the national anniversary in 2026.

Other names have also appeared in discussions of the event, including sestercentennial, quarter millennium, and bisesquicentennial. Semiquincentennial is the clearest and most widely used official-style term, especially in the name of the United States Semiquincentennial Commission.

The terminology is easy to mix up with bicentennial, which means 200 years, and sesquicentennial, which means 150 years. The United States celebrated its bicentennial in 1976, exactly 50 years before the America250 observance.