"O Flautista", Candido Portinari
Choro (Portuguese pronunciation: [ˈʃoɾu], "cry" or "lament"), traditionally called chorinho ("little cry" or "little lament"), is a Brazilian popular music instrumental style. Its origins are in 19th century Rio de Janeiro. In spite of the name, the style often has a fast and happy rhythm, characterized by virtuosity and improvisation. Choro is considered the first urban popular music typical of Brazil.
Instruments commonly played in choro
Originally choro was played by a trio of flute, guitar and cavaquinho (a small chordophone with four strings). Other instruments commonly played in choro are the mandolin, clarinet, saxophone, trumpet and trombone. These melody instruments are backed by a rhythm section composed of guitar, 7-string guitar (playing bass lines) and light percussion, such as a pandeiro. The cavaquinho appears sometimes as a melody instrument, other times as part of the rhythm.
Structurally, a choro composition usually has three parts, played in a rondo form: AABBACCA, with each section typically in a different key. There are a variety of choros in both major and minor keys.
In the 19th century, choro resulted from the style of playing European musical genres (polka, schottische, waltz, mazurka) by carioca musicians, who was already strongly influenced by African rhythms, principally the lundu and the batuque. Originally the term "Choro" referred to the music style of these ensembles (e.g. in the 1870’s flutist Joaquim Antônio da Silva Callado formed an ensemble called "Choro Carioca"), and later the term referred to the music genre of these ensembles. The accompanying music of the Maxixe (dance) (also called "tango brasileiro") was played by these choro ensembles.
Just like ragtime in the United States, choro springs up as a result of influences of musical styles and rhythms coming from Europe and Africa.
Much of the mainstream success of this style of music came from the early days of radio, when bands performed live on the air. By the 1950s and 1960s it was replaced by urban samba in radio, but was still alive in amateur circles called "rodas de choro" (choro gatherings in residences and botecos). In the late 1970s there was a successful effort to revitalize the genre in the mainstream, through TV-sponsored nation-wide festivals in 1977 and 1978, which attracted a new, younger generation of profissional musicians. Thanks in great part to these efforts, choro music remains strong in Brazil. More recently, choro has attracted the attention of musicians in the United States, such as Mike Marshall and Maurita Murphy Mead, who have brought this kind of music to a new audience.
Most Brazilian classical composers recognize the sophistication of choro and its major importance in Brazilian instrumental music. Radamés Gnattali said it was the most sophisticated instrumental popular music in the world. Heitor Villa-Lobos defined choro as the true incarnation of Brazilian soul. Notably, both composers had some of their music inspired by choro, bringing it to the classical tradition. The French composer Darius Milhaud was enchanted by choro when he lived in Brazil (in 1917) and he composed the ballet Le Boeuf sur le toit, in which he quotes close to 30 Brazilian tunes. 
According to Aquiles Rique Reis (a Brazilian singer), ”Choro is classical music played with bare feet and callus on the hands”
Notable Brazilian choro musicians
Notable choro compositions
Livingston-Isenhour, T., and Garcia, T. G. C. (2005). Choro: A Social History of a Brazilian Popular Music. Bloomington, Indiana: Indiana University Press.
2005 - Brasileirinho: Grandes Encontros do Choro. Directed by Mika Kaurismäki.