I am using the following definition for mean reversion I found on the web:

"Reversion to the mean is the statistical phenomenon stating that the greater the deviation of avariate from its mean, the greater the probability that the next measured variate will deviate less far. In other words, an extreme event is likely to be followed by a less extreme event."random

My friend insists there is no requirement for randomness and uses a similar definition of mean reversion but without the word "". The application is using mean reversion for the pricing of commodities.random

So, isa necessary condition for mean reversion?randomness

Is there a better definition of mean reversion?

How can I convince my friend that mean reversion only applies to random variables?

Thanks in advance.