Ancient nature being and divine counterpart, frequently of colossal stature.

Jötnar are a collective of beings inhabiting Jotunheim and Útgarðr. They are not simply evil but represent chaotic natural forces that the gods must negotiate with, defeat, or marry.

Many gods partially descend from jötnar: Odin is the grandson of the jötunn Bölþorn, and Thor fathers children with the giantess Járnsaxa. The boundary between gods and jötnar is consistently fluid in eddic mythology.

Attestations

John Lindow, Norse Mythology: A Guide to the Gods (2001)
Systematic survey of the jötnar's role in Norse mythology.