Original: Taken together, the Khordeh Avesta is considered the prayer book for general lay use. In a wider sense, the term Khordeh Avesta includes all material other than the Yasna, the Visparad and the Vendidad, as it is only the ceremonies contained in these three books that are reserved for the priests.
Simplified: Other parts of Avesta are named Yasna, Yashts, Visperad, Vendidad and Khordeh Avesta.