Here are a few examples of bluegrass music.
In the third video the musicians explain that bluegrass is a new form of music that really began in the 1950s after jazz, blues, and after country music.
My favorite country singer was Hank Williams.
This is an example of blues music from the Mississippi delta.
Before blues we have jazz. Improvization is the heart of jazz. In this song saxophonist Charlie Parker plays a familiar tune/song by George Gershwin.