Bluegrass

Bluegrass music is a form of American roots music, and is a sub-genre of country music. It has its own roots in Irish, Scottish, Welsh and English traditional music. Bluegrass was inspired by the music of immigrants from the United Kingdom and Ireland (particularly the Scots-Irish immigrants in Appalachia), as well as jazz and blues. In bluegrass, as in jazz, each instrument takes its turn playing the melody and improvising around it, while the others perform accompaniment. This is in contrast to old-time music, in which all instruments play the melody together or one instrument carries the lead throughout while the others provide accompaniment. Traditional bluegrass is typically based around acoustic stringed instruments, such as mandolin, acoustic guitar, banjo, fiddle, and upright bass, with or without vocals.

Source : http://en.wikipedia.org/wiki/Bluegrass_music