on Just Publishing Advice:

What is KENP? For new Amazon authors, it an important acronym to understand.
KENP stands for Kindle Edition Normalised Pages. Amazon uses the process as the formula to calculate the number of ebook pages read by a Kindle Unlimited subscriber.
For every page of your ebook that a reader reads, you earn royalties.
Amazon determines the amount month-to-month, which depends on the size of its Global Fund.