J.R.R. Tolkien identifies the Black Speech as the language of Mordor in The Lord of the Rings.
Sauron created the Black Speech during the Second Age as a language for his servants and as a possible common tongue for the forces under his control. It is associated with Mordor, although Tolkien’s notes indicate that not every servant of Sauron necessarily used it in everyday communication.
The best-known example appears on the One Ring. The inscription is written in Tengwar characters, but the words themselves are in Black Speech: “Ash nazg durbatulûk, ash nazg gimbatul,” followed by lines about ruling and binding the Rings of Power.
Black Speech is often confused with Quenya or Sindarin, Tolkien’s major Elvish languages. Quenya is an ancient, formal Elvish language, while Sindarin is the commonly spoken Elvish language of much of Middle-earth. The script and language are also different: Tengwar is a writing system, not the Black Speech itself.