Short answers, pulled from the story.
An accordion is a box-shaped, bellows-driven free-reed aerophone musical instrument. It produces sound when the player compresses or expands the bellows, forcing air across strips of brass or steel called reeds, which vibrate inside the body. The right-hand keyboard normally plays the melody and the left-hand buttons play the accompaniment.
An instrument called the accordion was first patented by Cyrill Demian in Vienna in 1829. The basic form of the instrument is believed to have been invented earlier, in Berlin in 1822, by Christian Friedrich Ludwig Buschmann, though one instrument discovered in 2006 appears to have been built before that.
The word accordion comes from the 19th-century German Akkordeon, which derives from Akkord, meaning musical chord or concord of sounds. The oldest name for this group of instruments was harmonika, from a Greek word meaning harmonic or musical.
A piano accordion uses a piano-style keyboard on its right-hand side, while a button accordion uses a buttonboard. Button accordions are further divided into chromatic and diatonic types, and diatonic button accordions tend to be bisonoric, producing different pitches depending on bellows direction.
China has the most accordionists in the world, and possibly more than every other country combined. The accordion was introduced to China in 1926 and grew popular thanks to Russian teachers and its use in the People's Liberation Army.
The accordion is used in folk, popular, classical, jazz, cajun, zydeco, klezmer, and rock music. It is central to genres such as vallenato and cumbia in Colombia, norteno in Mexico, forro and sertanejo in Brazil, merengue in the Dominican Republic, and Tejano, Creole, and polka music in the United States.
The golden age of the accordion refers to the period from the 1900s to the 1960s when the instrument appeared widely in popular music. Major influences during this half-century included Pietro Frosini, the brothers Guido and Pietro Deiro, and Charles Magnante.