Some Definitions of Jazz

Jazz is a music that originated at the beginning of the 20th century, arguably earlier [see blog author comment below], within the African-American communities of the Southern United States. Its roots lie in the adoption by African-Americans of European harmony and form, taking on those European elements and combining them into their existing African-based music. Its African musical basis is evident in its use of blue notes, improvisation, polyrhythms, syncopation and the swing note. From its early development until the present day, jazz has also incorporated elements from popular music especially, in its early days, from American popular music.

Definitions
Jazz spans a range of music from ragtime to the present day—a period of over 100 years—and has proved to be very difficult to define. Attempts have been made to define jazz from the perspective of other musical traditions—using the point of view of European music history or African music for example—but critic
Joachim Berendt argues that its terms of reference and its definition should be broader. Berendt defines jazz as a "form of art music which originated in the United States through the confrontation of blacks with European music" and argues that it differs from European music in that jazz has a "special relationship to time defined as 'swing'", involves "a spontaneity and vitality of musical production in which improvisation plays a role" and contains a "sonority and manner of phrasing which mirror the individuality of the performing jazz musician".

A broader definition that encompasses all of the radically different eras of jazz has been proposed by Travis Jackson: he states that it is music that includes qualities such as swing, improvising, group interaction, developing an 'individual voice', and being open to different musical possibilities. An overview of the discussion on definitions is provided by Krin Gabbard, who argues that "jazz is a construct" that, while artificial, still is useful to designate "a number of musics with enough in common to be understood as part of a coherent tradition". In contrast to the efforts of commentators and enthusiasts of certain types of jazz, who have argued for narrower definitions that exclude other types, the musicians themselves are often reluctant to define the music they play. Duke Ellington, one of jazz's most famous figures, summed up this perspective by saying, "It's all music".
  http://en.wikipedia.org/wiki/Jazz

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Note by the Blog Author
I was raised on live boogie-woogie music and very early rock and roll. It was said in those days (the 1950s), that jazz began as the prototype of ragtime, as walking-band funeral music. At a Black funeral in the deep South from about 1870 onward, a band would play a march as the mourners walked from the church to the gravesite. After the services at the grave were finished, the same band would change tempo and play something lively and positive as the mourners danced back to town. This is where the improvisation and handoffs to the various instruments come from. The fetching and eternal message of jazz is that "life goes on" even after the wrenching mourning of a beloved and departed person. The formal, musicological, reductionist definitions of jazz came much later –- and none of them completely fit that lively dance back to town and away from the gravesite.