The language devised by Sauron in the SecondAge for the communication between him and his servants. It died out at the end of the SecondAge, but was reintrodiced after he had taken shape again in the ThirdAge. In it's pure form it was only used by him and his close servants (i.e. the Nazgūl). The only given example of the pure black speech is the ring inscription:
Ash nazg durbatulūk, ash nazg gimbatul, ash nazg thrakatulūk agh burzum-ishi krimpatul.
One Ring to rule them all, One Ring to find them, One Ring to bring them all and in the Darkness bind them.
The Orcs spoke a debased form of it.