Jazz evolved and became an important genre of music over the course of the 20th century, and during the second half of that century, rock music did the same. Jazz is an American musical artform that originated in the beginning of the 20th century in African American communities in the Southern United States from a confluence of African and European music traditions. The style's West African pedigree is evident in its use of blue notes, improvisation, polyrhythms, syncopation, and the swung note.