nether region

noun nether regions · netherregion

1. Hell; a realm beneath the surface of the earth conceived as the abode of the souls of the dead and, sometimes, as the abode of demons or evil spirits. At this instant old Roger Chillingworth thrust himself through the crowd—or, perhaps, so dark, disturbed, and evil was his look, he rose up out of some nether region.

   Similar: Hades, netherworld, underworld

2. broadly A place which is subterranean or enclosed beneath a surface, especially one which is dark, dank, or otherwise inhospitable. But the steward of those nether regions marked him, by the electric lamps, as a lurking passenger to be watched; and wondered who, at that depth in the ship, could be carrying valuables.
3. euphemistic, humorous, sometimes The private parts between the legs; the groin or buttocks. The rash of celebrities flashing their nether regions worries Peter Post, director of the Emily Post Institute of etiquette and manners.