What is the meaning of Bluegrass?

Kentucky bluegrass, Poa pratensis.

A subgenre of country music with roots in Scots-Irish Appalachian folk music, blues, and jazz and characterized by banjos, fiddles, acoustic guitars, dobros, and mandolins; but containing no drums, electric guitars, pianos or other keyboard or wind instruments.

bluegrass

bluegrass (a style of country music)

Source: wiktionary.org