Jazz is certainly not America's only original music - Blues, Country, and Rock and Roll certainly all qualify as well. Different instruments, phrasing, rhythm, or harmonies can all define a new style of music, and there are literally thousands upon thousands of different styles. In classical music, for instance, the composer writes the notes on the page and the music is to be played the way the composer instructs. This mentality carries over to many forms of music, where fans prefer to hear their live music performed exactly like it was on the CD that they purchased. Here's how I interpret music.
Jazz has many forms.
Big band swing is one form using lots of structure in a large group setting. Rock-jazz fusion has more qualities of instrumental rock. Hot jazz has a swagger reminiscent of New Orleans funeral marches. However, all of them have the improvisation quality that makes jazz unique from all other forms of music. Because of improvisation, jazz is quite often bittersweet.