The Northern Waste was a cold and icy region in the far north end of Middle-earth, located above Mount Gundabad and the Ered Mithrin. It was composed mostly of snow and ice; however it did have several great frozen lakes, and a few unfrozen lakes that had bitterly cold waters. However there was life in this freezing cold region.
The Cold-drakes of the North, which drove the Dwarves out of the Grey Mountains, came from the Northern Waste. The Drakes killed Dain I and his son Frór outside their Halls in the Grey Mountains. The Dwarves then fled to Erebor and the Iron Hills It is likely that the "Goblins and Hobgoblins" that later colonized the Ered Mithrin drove most of the Cold Drakes back into the Northern Waste.
There were also men up in the wastes called the Lossoth. They lived in different tribes and were often at war with eachother, especially against the tribes in Forochel and Forodwaith. It is also said that some of the Northern Waste Tribes aided the Witch King during his destruction of Eriador. It was most likely because of their disliking of the the southern regions and out of fear. The less hostile Lossoth of Forodwaith and Forochel stayed neutral until the last king of Arnor (King Arvedui) came out of hiding in Mount Gundabad and asked for aid from the Lossoth of Forochel. They unwillingly aided him. He later took a ship through the Icebay of Forochel, but perished in a storm and sank to the bottom of the sea along with the palantir of the North.
It is also possible that this is where the Snow Trolls dwell. Snow Trolls never appeared in Tolkien's work but it is infered that they exist because there is an encription of one on the Horn of Helms Deep. It is likely that the king of Gondor made peace with the Lossoth of the Northern Waste, and the Dwarves reclaimed the halls in the Grey Mountains in the early fourth age.