The Jötnar (singular Jötunn) are an odd bunch, and difficult to define. Despite generally being translated as ‘Giants', they are usually the same size as humans.
Often said to be at war with the Gods of the Æsir and Vanir, nevertheless, many of the Norse Gods themselves are borne of one or more Jötunn. It's perhaps better to consider them as ‘devourers'; chaotic spirits of night and darkness and winter.
We'll get onto a few specific Jötunn later in this article but they include Hel – the Goddess/Giantess of the Underworld and Ymir who is a hermaphroditic entity that is the first being in the Norse creation myth.
Trolls are a subset of the Jötnar.