HUD display new graphic explanation ?

There appears to be a graphic I haven’t noticed before that occupies the very bottom of the screen for most or the width.  I can’t figure out to interpret it?? There’s a red averaging trend line along the top of the coloured bars. I’ve searched the manual but haven’t found an explanation . Anyone know?

The red line is your heart rate. Below that is your power output.  You can toggle that on or off by pressing the G on your keyboard.