Give some stream of consciousness and then the answer. A contour line (also isocline, isopleth, isarithm, or equipotential curve) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of the three-dimensional graph of the function f (x, y) parallel to the x, y plane. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines.

Answer this question: what is a contour line on a topographic map?
This is the relevant information: In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level.
Therefore, the answer is points of equal elevation ( height ) above a given level , such as mean sea level.