Health graphs explained?

Sorry if this has been answered, I can't find an explanation anywhere... I have the Body+ scales and in the Healthmate app, it shows you weight, body fat, muscle mass etc. I can't figure out the graphs; I can see my measurements, then there is also the trending line... but then there is also a shaded area on the graph and I don't know what it means, is it the range I should be aiming for?