As the term "jazz" has long been used for a wide variety of styles, a comprehensive definition including all varieties is elusive. While some enthusiasts of certain types of jazz have argued for narrower definitions which exclude many other types of music also commonly known as jazz, jazz musicians themselves are often reluctant to define the music they play. Duke Ellington summed it up by saying, "It's all music." Some critics have even stated that Ellington's music was not in fact jazz, as by its very definition, according to them, jazz cannot be orchestrated. On the other hand Ellington's friend Earl Hines's 20 solo "transformative versions" of Ellington compositions (on Earl Hines Plays Duke Ellington recorded in the 1970s) were described by Ben Ratliff, the New York Times jazz critic, as "as good an example of the jazz process as anything out there"
There have long been debates in the jazz community over the boundaries or definition of “jazz.” In the mid-1930s, New Orleans jazz lovers criticized the "innovations" of the swing era as being contrary to the collective improvisation they saw as essential to "true" jazz. From the 1940s and 1960s, traditional jazz enthusiasts and Hard Bop criticized each other, often arguing that the other style was somehow not "real" jazz. Although alteration or transformation of jazz by new influences has been initially criticized as “radical” or a “debasement,” Andrew Gilbert argues that jazz has the “ability to absorb and transform influences” from diverse musical styles.
Commercially-oriented or popular music-influenced forms of jazz have long been criticized. Traditional jazz enthusiasts have dismissed the 1970s jazz fusion era as a period of commercial debasement. However, according to Bruce Johnson, jazz music has always had a "tension between jazz as a commercial music and an art form" .
Gilbert notes that as the notion of a canon of traditional jazz is developing, the “achievements of the past” may be become "…privileged over the idiosyncratic creativity...” and innovation of current artists. Village Voice jazz critic Gary Giddins argues that as the creation and dissemination of jazz is becoming increasingly institutionalized and dominated by major entertainment firms, jazz is facing a "...perilous future of respectability and disinterested acceptance." David Ake warns that the creation of “norms” in jazz and the establishment of a “jazz tradition” may exclude or sideline other newer, avant-garde forms of jazz.
One way to get around the definitional problems is to define the term “jazz” more broadly. According to Krin Gabbard “jazz is a construct” or category that, while artificial, still is useful to designate “a number of musics with enough in common part of a coherent tradition”. Travis Jackson also defines jazz in a broader way by stating that it is music that includes qualities such as “ 'swinging', improvising, group interaction, developing an 'individual voice', and being 'open' to different musical possibilities”.
Where to draw the boundaries of "jazz" is the subject of debate among music critics, scholars, and fans. Music that is a mixture of jazz and pop music, such as the recent albums of Jamie Cullum, James Blunt and Joss Stone have been called "jazz" performers. Jazz festivals are increasingly programming a wide range of genres, including world beat music, folk, electronica, and hip-hop. This trend may lead to the perception that all of the performers at a festival are jazz artists – including artists from non-jazz genres.