This is a glossary list of opera genres, giving alternative names. "Opera" is an Italian word (short for "opera in musica"); it was not at first commonly used in Italy (or in other countries) to refer to the genre of particular works. Most composers used more precise designations to present their work to the public. Often specific genres of opera were commissioned by theatres or patrons (in which case the form of the work might deviate more or less from the genre norm, depending on the inclination of the composer). Opera genres are not exclusive. Some operas are regarded as belonging to several.