What was Moria originally called in J.R.R. Tolkien’s legendarium?

Moria was originally called Khazad-dûm in J.R.R. Tolkien’s legendarium.

Khazad-dûm was the greatest and most famous realm of the Dwarves. It lay beneath the Misty Mountains and was renowned for its immense halls, mines, wealth, and production of mithril. The name means “Dwarrowdelf” in Tolkien’s translation, combining the ideas of the Dwarves and their excavated dwelling.

The realm was abandoned after the Dwarves delved too deeply and awakened a Balrog, later known as Durin’s Bane. The creature killed King Durin VI in the Third Age, and his successor Náin I was also killed. The survivors fled, leaving the underground city in darkness.

By the time of The Lord of the Rings, the name Moria is associated with the ruined, dangerous realm. The Fellowship passes through it while traveling under the mountains. Khazad-dûm and Moria therefore refer to the same place at different stages of its history.