Read any book published on jazz. Learn about the rhythm patterns and improvisational techniques that define the genre. Learn about the history of jazz music and it's cultural relevance, with regard to the largely African-American community that created it.
Listen to several jazz recordings by one musician. Then listen to several recordings by at least two others that perhaps play different instruments. For example: alto sax, trumpet and piano. You will notice that there are many different styles. But it is that individuality is that unifies the form.
Feel the music that you listen to. Above all else jazz is an emotionally expressive form of music. Whereas classical is, emotional, yet structured, jazz exists moment to moment. Each player's personal sound becomes his or her identity. That's what makes up the music, not the uniformity of instruments desired in classical arrangement. Jazz is defined by its improvisation.
Watch a live jazz performance at a real jazz club. Again, feel the music that you listen to. But also feel the emotions of he artist as he is playing. If it is good, you will get a sense of the artist behind the instrument. Watch how the people react to the music and how they interact with each other. The connection between artist, instrument and crowd are crucial. The crowd picks up on the improvisation. None of the crowd will be tapping their foot of fingers to the same notes; everyone improvising the music in their head and their hearts, interpreting where they think it should go and what it means to them.
Reflect on your experience of reading about jazz. As well as listening to jazz music and hanging around jazz enthusiasts. Examine your own opinions about what jazz means. Whatever your opinion is, is correct. Jazz is what you believe it to be. Like all true art forms, there is no technical explanation that defines the line between craft and art. Art is whatever touches you. By experiencing jazz, you will come to know what it means to you. Whatever that is is what jazz means.