The slope resistance of a Zener diode refers to the change in voltage over the change in current in the reverse bias region, representing a form of resistance. This slope is derived from the current versus voltage plot, where the Zener diode begins to conduct in reverse bias. It is not a fixed value but can be averaged over a specific range of reverse bias conditions. The concept helps in understanding the diode's behavior in voltage regulation applications. Overall, slope resistance is a crucial parameter for analyzing Zener diode performance in circuits.