In Norse mythology, giants are the original “founding” beings at the top of the Norse family tree. The more commonly known gods (such as Odin, Thor) are all direct or indirect descendants of these giants. Giants were called Jötunn (singular) or Jötnar (plural). The word Jötunn originally came from the Proto-Germanic word that meant “devourer.”
Another name for them was þursar or þurs (pronounced thurss), which means something like “powerful and injurious one” or simply something like “piercer” or “thorn.” In the rune poems, the Thurisaz rune is associated with the Jötnar (giants), as well as sickness, tragedy, and pain.
The very first giant, Ymir (pronounced EE-mir), arose from primordial chaos when the worlds of fire and of ice came together in a tremendous, hissing scream. His offspring, the Jötnar, were spirits of this chaos, representing the destructive cycle of the natural universal order.
The Aesir and the Vanir tribes of gods also arose partially from this same race of giants (though they also had another ancestor, Buri – a being of unknown origin that had been bounded in ice until he was eventually set free from Ymir’s cow named Auðumbla who licked at the ice for three days). By the gods’ own nature and choice, the giants became the positive or creative aspect of universal order. In Viking lore, it is not so much that the gods are good and the giants evil, but rather that the gods and giants are in opposition and balance. This is not to say that Norse belief observed a strict dualism (as some ancient religions did), but they understood their world through their stories of struggle between the gods and the Jötnar, between creation and destruction,
Sometimes, the difference between giants and gods is itself obscure. For example, Loki is often thought of as the Viking god of trouble. He was an adopted member of the Aesir tribe of gods and blood-brother to Odin, but Loki was the son of giants and is only ambiguously called a god in the primary sources. None of his offspring are gods but are giants or supernatural beasts. Similarly, Jörð (a “Mother Earth” figure) and Skadi (the ski-borne goddess of the wild) appear in the Eddas as Jötunn in origin. They are later called goddesses, but then often excluded from lists or gatherings of goddesses in Asgard.
Some experts see in this interplay between gods and giants a parallel of how the Vikings themselves interacted with the cultures around them. Whether this is accurate or not, the lore is clear that the gods and giants are not distinct races of beings but rather opposing and competing forces. These competing forces’ cosmic nature can easily be inferred from the names, attributes, and actions of the individual members within these “warring tribes.”
Source: Sons of Vikings