fillsteps

     plot <data> with fillsteps {above|below} {y=<baseline>}

The fillsteps style is only relevant to 2D plotting. It is exactly like the style steps except that the area between the curve and the baseline (default y=0) is filled in the current fill style. The options above and below fill only the portion to one side of the baseline. Note that in moving from one data point to the next, both steps and fillsteps first trace the change in x coordinate and then the change in y coordinate. See steps.