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 
