A barbarous name is a meaningless or seemingly meaningless word used in magic rituals. The term barbarous comes from the Greek barbaroi meaning those who do not follow Greek customs, barbarian. Often these names were derived from foreign sources and acquired their "barbarous" nature from the magician's lack of understanding of that language.
One example includes the meaningless magical curse words frequently employed on Roman "defixiones", or curse tablets of the sort which were thrown in sacred spring waters like those found in Aquae Sulis, the Roman site of Bath, England. This type of word, such as "Bazagra", "Bescu" and "Berebescu", are seemingly of Etruscan origin, and were intended to lend magical power to the curse. These curses were frequently intended to acquire a divinity's aid in punishing or seeking vengeance on one's enemies.
Other examples better known in the modern era include Abracadabra and Hocus Pocus.
Compare the history of "Baphomet".