In Norse mythology, Ifing (Old Norse, Ífingr) is a significant river that serves as a natural boundary, separating Asgard, the realm of the gods, from Jotunheim, the land of giants. This description is found in stanza 16 of the poem Vafthrudnismal from the Poetic Edda. The stanza reads:
"Ifing the river is called, which divides the earth
between the sons of giants and the gods;
freely it will flow through all time,
ice never forms on the river."
— Larrington translation
According to John Lindow in Norse Mythology (2001), the river Ifing is characterized by its swift-flowing waters, which prevent ice from forming on its surface. This swiftness makes it extremely challenging to ford or cross, thus serving as an effective natural barrier between the realms of the gods and the giants.