Electrical installation diversification
I suspect that terminology may be a local one but you have no location in your user profile.

To me the most likely reason is for calculating total load on a system such as a transformer feeding a group of houses.


Cookers will be used at somewhat diverse1 times and for diverse durations by each household so the expected average and peak load will be a significant factor less than the sum of all the cookers.
Air conditioning is very likely to be non-diverse as each home will experience the same heat input on a warm day and all AC units will turn on around the same time and for many hours at a time. The peak load will be the sum of all the AC units.




1 (/dʌɪˈvəːs,ˈdʌɪvəːs/
adjective
showing a great deal of variety; very different.
Synonyms:   various, many and various, sundry, manifold, multiple)