What does the slope represent if the voltage vs current value graph

If the voltage is on the x-axis and the current is on the y-axis,

then the slope of the curve represents the resistance of the

device that the voltage is being applied to.

If the graph is NOT a straight line, then it gets more interesting.

It shows that the resistance of the device or component is not

constant, but depends on the voltage applied to it. A diode is

a good example of that. The voltage/current graph of a diode

has sudden changes of slope ... nothing gentle about it.