What is the physical meaning of the slope for the static frictional force vs. normal force graph?

So having a slope refers to a surface that is not level and allows gravity to move an object in the direction of gravity's pull, which on the surface of the earth, is known as down. The physical interpretation of mathematical slope is similar. A slope of zero is equivalent to level - no marble movement.

Friction force is equal to the coefficient of friction times the normal force:

F = μN

So on a graph of Fs vs. N, the slope of the line is the coefficient of static friction.