Each area represents how much a person was mentioned.
However, it does not mean that the top (purple) got heaps more mentions than the bottom (orange). The very top line is basically tracking the cumulative mentions for all three people you've selected.
It looks like orange had consistent mentions throughout the selected time period, whilst pink had periods of no mentioning (12/9-20/9), as did purple (14/9, 18/9-20/9).
That's if they're using these graphs correctly, though.
-beardymac, residential Statistical Mathematics student.