what is meant by the word "blues" in the title? what are Sonny's blues?

James Baldwin 's "Sonny's Blues" is the story of a young jazz musician (Sonny) from Harlem, NY who gets addicted to heroin, is arrested for using and selling drugs, and returns to his childhood neighborhood after his release from prison.

The word "blues" is a play on the term. Sonny deffinately has his share of sad times (blues) as well the word plays on the whole jazz "blues" concept.