Bluegrass music is a type of American roots music which is a sub-genre of country music. It also has its own roots in English, Scottish and Irish music. Bluegrass was inspired by the music of immigrants from the United Kingdom, as well as in Ireland; specifically among the Scots-Irish immigrants in Appalachia. It even links itself to jazz and blues. With bluegrass music, each instrument takes a turn playing the melody and improvising around it while the other instruments play accompaniment. The basic musical instruments used in bluegrass are the acoustic guitar, banjo, fiddle, mandolin, and the upright bass; also referred to as the "Dog House" bass.
Two things that make bluegrass music unique is that it relies mostly on acoustic instruments and a vocal harmony which may feature two, three, or four parts; which in turn, features a dissonant or modal sound in the highest voice. This style has been characterized as the "High Lonesome Sound". Many of the folks that grew up playing bluegrass music did so without electricity, hence the acoustic instruments. Many conservative country music people still frown upon the use of electrical instruments in bluegrass.
The term "BLUEGRASS" came from the "Father of Bluegrass" Bill Monroe and his "Blue Grass Boys". Monroe named his band in honor of his home state of Kentucky. No one person can be said to have 'invented' bluegrass music because it is a combination of country, old-time, jazz and ragtime. Bill Monroe formed his band, the Blue Grass Boys, in 1939; but it wasn't until 1945, when banjo great Earl Scruggs and his three-finger style playing joined, that bluegrass began to develop.
From 1946 to 1948, Bill Monroe's band featured, along with Scruggs on banjo, Lester Flatt on guitar, Chubby Wise on fiddle, and "Cedric Rainwater" (Howard Watts) on bass; while Monroe played mandolin. This group has been considered the "original bluegrass band" which created the instrumental configuration and definitive sound that remains a model for bluegrass music to this day.