Blues is a vocal and instrumental form of music based on the use of "blue notes." It emerged in Black communities of the United States from spirituals, work songs, field hollers, shouts and chants, and rhymed simple narrative ballads. The use of blue notes and the prominence of call-and-response patterns in the music and lyrics are indicative of African influence.
"Blue notes," also known as "worried notes," are the typically flattened third, fifth, and seventh degrees in a major scale. This is what gives the blues its inherent minor tonality. From performer to performer, or from blues genre to genre, e.g., country blues, the deviation of the "blue note" from the actual scale can be greater.
The blues influenced much of later American and Western popular music. It became one of the roots of jazz, rhythm and blues, and bluegrass. During the 1960s and 1970s, a hybrid form of the blues, blues rock, developed by combining of blues with various rock and roll forms.