Median Level:

• The median level of a set of points is a line that has half the points above and half the points below.
• The median level of a set of lines, is a line that has half the lines above and half the lines below.

Median level of a set of points

Median of a set of lines.
The thick dark blue line and the thick red line are the median level of the blue and red line sets respectively.  If you follow along the lines, at every point there is exactly half of the lines and half of the lines below.

The median line is always the same line at the very beginning and at the very end.   BUT in between it is not necessarily the same line.