Throughout its recent history, evolution and contemporary route, jazz music has been identified with improvisation.
One point in which jazz differentiates against other musical idioms (that also share the element of improvisation) is that improvisation in jazz is not a static “snapshot” nor is a purpose.
We could say that improvisation is the very language of jazz.
The jazz musician deals with a musical piece, that constitutes the medium, which he/she uses as a motivation in order to express himself/herself, to expand his/her boundaries and imagination, to take risks, to be creative and of course to get into a musical dialogue with the other musicians!
One could compare this situation to the testing of a rope walker, who keeps his balance, having been practicing with discipline on the technique but without being able to predict what exactly is gonna happen on that rope, during the show!
The musical score (usually a jazz standard) is a kind of “canvas”, on which the musician will almost recompose its components (phrasing the theme, reviewing its harmony, improvising its melody, changing its time signature, etc), will interact with the rest of the group and will improvise, having mastered the piece's form, while respecting its current arrangement, style and context.

As with every other instrument, the voice shares the same field of action.
The jazz singer must always be alert, being able to rhythmically move with freedom within the form of a piece (phrasing the theme), changing-improvising the melody, having the ears wide open while keeping a constant conversation with the other musicians and improvise with imagination and inventiveness, having the musical context and style of the piece, always in consideration.

In jazz singing, the voice is a musical instrument.
And in jazz music, the significance lies also on how... not only on what.

Jazz is a common universal language, that throughout its history has proven its power to evolve, to bring musicians together (who have the unique ability to play and communicate musically, without even knowing each other beforehand!) and of course to unite civilizations from every part of the planet, under the inspirational force of continuous artistic creation.