Vappu is a diminutive form of the name Valpuri, which is of Finnish origin. The name Valpuri itself is derived from the name Walpurga, a saint known for her efforts in converting the local populace to Christianity and her battles against pestilence and witchcraft. The name is closely associated with Walpurgis Night, a traditional spring festival celebrated on the night of April 30th, which honors Saint Walpurga and involves various customs such as lighting bonfires to ward off evil spirits.