A wait state is a delay experienced by a computer processor when accessing external memory or another device that is slow to respond.
Even memory, the fastest of these, cannot supply data as fast as the CPU could process it.
Some second-level CPU caches run slower than the processor core.
Wait states can be used to reduce the energy consumption of a processor, by allowing the main processor clock to either slow down or temporarily pause during the wait state if the CPU has no other work to do.
Rather than spinning uselessly in a tight loop waiting for data, sporadically reducing the clock speed in this manner helps to keep the processor core cool and to extend battery life in portable computing devices.