Khazad-dûm is the underground Dwarf realm beneath the Misty Mountains in J.R.R. Tolkien’s works. The name is in Khuzdul, the language of the Dwarves, and means “Dwarrowdelf” in Tolkien’s English rendering.
Men and Elves more commonly call the place Moria. It was once the greatest mansion of the Dwarves, famous for its wealth and especially for mithril, a valuable fictional metal found beneath the mountains. Its mines and halls became central settings in The Lord of the Rings.
The Dwarves abandoned Khazad-dûm after awakening a Balrog, a powerful being associated with the ancient enemy Morgoth. By the time the Fellowship enters, the realm is deserted and dangerous. The expedition’s passage through Moria includes the Chamber of Mazarbul, the Bridge of Khazad-dûm, and Gandalf’s confrontation with the Balrog.
Erebor is the Lonely Mountain, while Gondolin was an Elven city and Angband was Morgoth’s fortress. Those names belong to different places and peoples.