Jazz

Jazz is a music genre that began in the African American communities of New Orleans in the late 1800s and early 1900s with roots in blues, ragtime, European harmony, African rhythmic traditions, spirituals, hymns, marches, and dance music (Wikipedia, n.d.-a). Think of jazz like a stew instead of a single ingredient. It took blues, ragtime, brass band marches, and church music, and simmered them together into something new.
Wikipedia

Two features set jazz apart from most other music. First, it relies on improvisation, meaning musicians make up parts of the music on the spot rather than just playing from sheet music. Second, it has a distinct rhythmic feel, built on syncopation and "swing," where the beat is played with a loose, rolling bounce instead of a strict, even count. The genre is also known for blue notes, complex chords, call and response between musicians, and interlocking rhythms called polyrhythms (Wikipedia, n.d.-b).
Wikipedia

Jazz did not stay in one form for long. Early jazz was dance music played by big bands, but over time the dance element faded and improvisation became the central focus (AllMusic, n.d.-a). That shift is a bit like a recipe that starts out as comfort food and slowly turns into fine dining, less about function and more about the skill of the cook. This evolution produced many branches: the fast, complex rhythms of bebop, the relaxed harmonies of cool jazz, the abstract, rule-breaking sound of free jazz, and the groove-heavy style of soul jazz (AllMusic, n.d.-a).
AllMusic
AllMusic

Jazz also blended with other genres over the decades. In the late 1960s and early 1970s, jazz fusion combined jazz improvisation with rock rhythms and electric instruments, and in the early 1980s a smoother, radio-friendly version called smooth jazz became popular (Wikipedia, n.d.-b). Despite all these changes, what has always tied jazz together is its foundation in the blues, group interplay among musicians, and unpredictable improvisation (AllMusic, n.d.-a).

AllMusic. (n.d.-a). Jazz music genre overview. https://www.allmusic.com/genre/jazz-ma0000002674
Wikipedia. (n.d.-b). Jazz. In Wikipedia. https://en.wikipedia.org/wiki/Jazz