The Dwarves speak Khuzdul in J.R.R. Tolkien's Middle-earth.
Khuzdul is the secret language of the Dwarves, who call themselves the Khazâd. Tolkien gives it a distinctive linguistic identity separate from the Elvish languages. Dwarves generally keep Khuzdul private, so relatively few words and phrases appear in the published narratives.
The best-known example is the inscription on the tomb of Balin in Moria: “Balin son of Fundin, Lord of Moria.” The battle cry “Baruk Khazâd! Khazâd ai-mênu!” is another famous Khuzdul phrase associated with Dwarven warfare.
Khuzdul is sometimes mistaken for a general name for all languages spoken underground, but it specifically refers to the Dwarves' own tongue. Tolkien developed it partly with the sound of Semitic languages in mind, while keeping its fictional history within Middle-earth.