1) April observance 2) German folklore 3) Supernatural legend 
Walpurgis Night is the English translation of Walpurgisnacht, the German name for the night of 30 April, so called because it is the eve of the feast day of Saint Walpurga, an 8th-century abbess in Germany. In German folklore Walpurgisnacht is believed to be the night of a witches` meeting on the Brocken, the highest peak in the Harz Mountains, a....
[n] - eve of May Day
noun eve of May Day