The word "mazoku" is written in kanji with the characters for "demon; evil, unnatural" and "family, race". (The "ma" is the same character as in "mahou", or "magic". Magic is then "the practice of the unnatural".)
In the Slayers world, there is a definite power structure among the Mazoku. At the top of this structure is the great Dark Lord Ruby Eye, also known as Shabranigdo. Below Shabranigdo in the hierarchy of Mazoku are five Mazokuou, or Demon Lords. They are Dynast Graushellar (Haou Graushellar), Beastmaster Xellas Metallium (Juuou Xellas Metallium), Hellmaster Phibrizo (Meiou Phibrizo), Demon Dragon Lord Gaav (Maryuuou Gaav), and Sea Lord Dolphin (Kaiou Dolphin). Each of the Mazokuou usually has one priest and one general. The notable exception is Xellas, who merely has an uberpowerful priest, Xelloss. There are many more various Mazoku that are more or less affiliated with one of the great lords, as well as lesser demons that they sometimes command.