On the 100th anniversary of the word “jazz,” we consider the question everyone was asking back then: “What Is jazz?” This diverse and diverting program looks at the many ways jazz has crossed paths with traditional concert music, in works ranging from Gershwin to Bernstein to Coltrane to Wynton Marsalis’s String Quartet (At the Octoroon Balls) to Francis Poulenc’s raucous music hall entertainment for nine, Le balmasqué(The Masked Ball).