Tolkien calls the language used by Sauron in The Lord of the Rings the Black Speech.
The Black Speech was created by Sauron during the Second Age for the servants of Mordor. Tolkien describes it as a language associated with the Dark Lord and his realm, rather than as a normal everyday language shared across Middle-earth.
Its best-known surviving example is the inscription on the One Ring: “Ash nazg durbatulûk, ash nazg gimbatul...” The inscription is written in Tengwar characters but uses the Black Speech of Mordor. This distinction matters because a writing system and a language are not the same thing.
Readers sometimes confuse the Black Speech with Orc languages or with Westron, the Common Speech. Tolkien gives the Black Speech a specific role and vocabulary, while many Orcs also use varied local forms of speech.