What rare alternate name for April Fools' Day appears in Wikipedia's lead?

The rare alternate name for April Fools' Day is All Fools' Day.

The name appears in the lead of Wikipedia's article as an uncommon synonym, alongside the more familiar forms “April Fools' Day” and “April Fool's Day.” The holiday is observed on 1 April and is associated with practical jokes, hoaxes and playful deception.

“All Fools' Day” should not be confused with the medieval Feast of Fools, a separate festival involving role reversals and mock religious ceremonies. Nor is it the same as the April-fool traditions known in France as poisson d'avril, or “April fish.”

The broader history of the holiday is uncertain. Proposed explanations connect it to calendar changes, older spring festivals and literary references, but no single origin has been proved. The alternate name is therefore a naming fact, not evidence of a settled historical explanation.