Answer: The population curves for predator and prey are not synchronized with each other and their amplitudes differ (the simple definition).
Step-by-step explanation: The slightly longer explanation is that changes in the prey population will not result in immediate or exactly identical changes in the predator population.
In the attached image, the red line represents the prey population and the blue the predator population. As it can be observed, when the prey population increases in size, the predator population size increases too.
However, this increase is not of the same size and is delayed in time. The predator population will continue to increase even though the prey population has started to decrease.
This has to do with the fact that the adult predators mated and gave birth when the food availability was still high. However, these new young individuals will not survive and reproduce due to decreasing prey. As the prey continues to decrease, more and more predators will perish.
The same cycle will then repeat over and over again.