Blues is a music genre and musical form originated by African Americans
in the Deep South of the United States around the end of the 19th century.
The genre developed from roots in African musical traditions,
 African-American work songs, spirituals, and European folk music.
 Blues incorporated spirituals, work songs, field hollers,
 shouts, chants, and rhymed simple narrative ballads.
 The blues form, ubiquitous in jazz,  rhythm and blues and rock and roll
 is characterized by the call-and-response pattern, the blues scale
and specific chord progressions, of which the twelve-bar blues
is the most common.
Blue notes,, usually thirds or fifths flattened in pitch,
 are also an essential part of the sound.
 Blues shuffles or walking bass reinforce the
 trance-like rhythm and form a  repetitive effect
 known as
THE  GROOVE