Classical music is art music produced or rooted in the traditions of Western culture, including both liturgical (religious) and secular music. While a more precise term is also used to refer to the period from 1750 to 1820 (the Classical period), this article is about the broad span of time from before the 6th century AD to the present day, which includes the Classical period and various other periods.
What is jazz? According to Wynton Marsalis jazz is music that swings. According to Pat Metheny jazz is not the music of Kenny G. According to Webster's jazz is characterized by propulsive syncopated rhythms, polyphonic ensemble playing, varying degrees of improvisation, and often deliberate distortions of pitch and timbre.
Rap is important because it's probably the most internationally recognized form of American popular music. Rap and hip-hop are performed throughout the world and in just about every language that you can imagine. The hip-hop subculture that rap is a part of is one of the most influential and controversial manifestations of American culture.