The fsteps style is only relevant to 2D plotting. It connects consecutive
points with two line segments: the first from (x1,y1) to (x1,y2) and the
second from (x1,y2) to (x2,y2). The input column requires are the same as for
plot styles lines and points. The difference between fsteps and steps
is that fsteps traces first the change in y and then the change in x.
steps traces first the change in x and then the change in y.
See also
http://www.gnuplot.info/demo/steps.htmlsteps demo.