A curve in two dimensions on which the value of a function 
is a constant. Other synonymous terms are equipotential
curve, isarithm, and isopleth. A plot of several contour lines is called a contour plot.
Contour Line
See also
Contour, Contour Plot, Equipotential CurveExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Contour Line." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ContourLine.html