Final answer:
The term 'third stream' was coined by Gunther Schuller in 1957, reflecting his vision for a fusion between jazz and classical music.
Step-by-step explanation:
The term third stream was introduced in 1957 by Gunther Schuller, who, for a time, believed that jazz and classical music should be treated as separate but congenial entities. The concept proposed a genre that is a fusion between jazz and classical music, aiming to take the improvisational aspects of jazz and combine them with the structured compositions of classical music. This attempt to blend the two distinct musical styles was reflective of a broader trend in the arts where creators were not afraid to challenge norms, as seen in the progressive works of composers like Berlioz, Strauss, and Wagner. During the same era, in the United States, the independence of black writers and musicians made significant cultural contributions, shaping the landscape of music, with Jazz emerging from the African American communities, and figures like W. C. Handy contributing to its development.