May 1: as a traditional spring festival, often celebrated by dancing around a maypole, crowning a May queen, etc.; as a more recent international labor holiday, observed in many countries by parades, demonstrations, etc.
See May Day in American Heritage Dictionary 4
noun
May 1, observed in the United States, Canada, and parts of Western Europe in celebration of the coming of spring.
May 1, observed as a holiday especially in socialist countries in honor of labor and labor organizations.