modern jazz n (Jazz) any of the styles of jazz that evolved between the early 1940s and the later emergence of avant-garde jazz, characterized by a greater harmonic and rhythmic complexity than hitherto Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014