Harmonium in the context of Indian harmonium

Accordions (from 19th-century German Akkordeon, from Akkord—"musical chord, concord of sounds") are a family of box-shaped musical instruments of the bellows-driven free reed aerophone type (producing sound as air flows past a reed in a frame). The essential characteristic of the accordion is to combine in one instrument a melody section, also called the diskant, usually on the right-hand keyboard, with an accompaniment or Basso continuo functionality on the left-hand. The musician normally plays the melody on buttons or keys on the right-hand side (referred to as the keyboard or sometimes the manual), and the accompaniment on bass or pre-set chord buttons on the left-hand side. A person who plays the accordion is called an accordionist.

The accordion belongs to the free-reed aerophone family. Other instruments in this family include the concertina, harmonica, and bandoneon. The concertina and bandoneon do not have the melody–accompaniment duality. The harmoneon is also related and, while having the descant vs. melody dualism, tries to make it less pronounced. The harmonium and American reed organ are in the same family, but are typically larger than an accordion and sit on a surface or the floor.

Chord organ is a kind of home organ that has a single short keyboard and a set of chord buttons, enabling the musician to play a melody or lead with one hand and accompanying chords with the other, like the accordion with a set of chord buttons which was originated from a patent by Cyrill Demian in 1829, etc.

Initially, the chord organ was invented as a kind of electronic home organ by Laurens Hammond in 1950. This was followed by the reed chord organ (c. 1959) and Optigan (c. 1971). The sound of the reed chord organ is somewhat similar to the harmonium or the accordion.

Christa Päffgen (German pronunciation: [ˈkʁɪsta ˈpɛfɡn̩]; 16 October 1938 – 18 July 1988), known by her stage name Nico, was a German singer, songwriter, actress and model.

Nico had roles in films including Federico Fellini's La Dolce Vita (1960) and Andy Warhol's Chelsea Girls (1966). At the insistence of Warhol, she sang lead on three songs of the Velvet Underground's debut album, The Velvet Underground & Nico (1967). At the same time, she released her debut album, Chelsea Girl (1967), composed of songs written by other musicians. At the suggestion of her friend Jim Morrison, she started writing her own material, using a harmonium, not traditionally a rock instrument. John Cale of the Velvet Underground became her musical arranger and produced The Marble Index (1968), Desertshore (1970), The End... (1974) and other albums.