Black Speech is the fictional language Tolkien created for Sauron and his servants. In The Lord of the Rings, Sauron devised it during the Second Age to serve as a common language among the forces of Mordor.
The best-known example is the inscription on the One Ring: “One Ring to rule them all,” written in the language’s poetic form. The inscription uses Tengwar letters, but the writing system and the language are different things; Tengwar is a script that can represent several languages.
Tolkien provided less surviving linguistic detail for Black Speech than for Quenya or Sindarin. Orcs often use different dialects rather than speaking one fully standardized language. This is why Black Speech should not be treated as the universal everyday language of every Orc in Middle-earth.