Definition of bluegrass
1
:any of several grasses (genus Poa) of which some have bluish-green culms;
especially
:kentucky bluegrass
2
[from the Blue Grass Boys, performing group, from Bluegrass state, nickname of Kentucky]
:country music played on unamplified stringed instruments (such as banjo, fiddle, guitar, and mandolin) and characterized by free improvisation and close usually high-pitched harmony 
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