This word is used both to describe one of the styles of "throat-singing" characteristic of folk music from Tuva (a style which sounds somewhat like a droning voice accompanied by a Theremin) and also to describe all Tuvan throat-singing styles (ranging from eathquake-like rumbling, to mid-tones with beats, and various high-register styles). All Tuvan throat singing involves the shaping of the mouth cavity to select overtones of the fundamental produced by the vocal folds, resulting in the simultaneous singing of multiple pitches.
The music is inspired by the steppes and the songs are often about horses, thus thematically Tuvan folk music is much like western cowboy music. The Xoomii techniques (and oriental language) makes the music sound alien to western ears, however.
Tuvan singing styles influenced the music of diverse cultures. In ancient times, Tibetan monks adapted their chanting to the subharmonics of Kargyraa, while in modern times, some American new age musicians impress with the otherworldly sounds of höömey and sygyt, inhumanly high-pitched yet not falsetto.
There's debate as to the exact number of styles or techniques the Tuvans use in their throat singing. The three principal styles are xoomii, kargyraa, and sygyt. Additional recognized styles include borbangnadyr, chylandyk, dumchuktaar, ezengileer, and kanzip. Some consider these additional styles to be variations or modifications of the three principal styles.