Short answers, pulled from the story.
Black Speech is the constructed language J. R. R. Tolkien created for the evil realm of Mordor in The Lord of the Rings. Sauron devised it to serve as the sole language of all his servants, though it fragmented into Orkish dialects and was never widely adopted outside Mordor.
The One Ring inscription is the only surviving text of pure Black Speech. It comes from the Rhyme of the Rings and reads: "Ash nazg durbatulûk, ash nazg gimbatul, ash nazg thrakatulûk, agh burzum-ishi krimpatul," meaning one ring to rule them all, one ring to find them, one ring to bring them all, and in the darkness bind them. Tolkien glossed each element of the inscription precisely.
Russian historian Alexandre Nemirovski argued that Black Speech bears a strong resemblance to Hurrian, an extinct agglutinative language of northern Mesopotamia. E. A. Speiser's Introduction to Hurrian appeared in 1941, around the time Tolkien was writing The Lord of the Rings, and Nemirovski identified parallel word elements in both languages, including durb- (to rule) and the Hurrian turob-, and gimb- (to find) with the Hurrian -ki(b).
Black Speech is 63% consonants, compared to 52% and 55% in two Elvish language samples, according to linguist Joanna Podhorodecka. Swedish linguist Nils-Lennart Johannesson found more sonorant sounds and more open syllables in Elvish than in Black Speech, concluding these differences were prominent enough to make Elvish sound pleasant and harmonious while Black Speech sounds harsh and strident.
A fan sent Tolkien a goblet engraved with the One Ring inscription in Black Speech. Because Tolkien regarded Black Speech as an accursed language and the Ring inscription in particular as a vile spell, he refused to drink from it and used it only as an ashtray.
David Salo used the limited existing Black Speech vocabulary to create two phrases for the film trilogy. He drew burzum-ishi and ashi from the Ring Verse, coined three additional abstract nouns using the -um suffix from the Ring Verse, and invented the remaining words himself.