A hellish dimension in Minecraft inhabited by potentially hostile mobs. It is accessible from the Overworld through a portal frame constructed of obsidian. Contains draconian terrain generation dominated by netherrack, absence of day/night cycle, fungi-based vegetation, and great oceans of lava. Do not try sleeping there.
Enderman, Skeleton, and Chicken (if ridden by a baby Zombie Pigman) can also spawn there.