What exactly does WordPress (Jetpack) Stats show?

I have seen a few discussions about how the numbers in Google Analytics and WordPress Stats differ, and after a few day of running Google Analytics I can see that mine do too. But unlike others I seem to get MORE pageviews on GA than on WS, though GA unique pageviews are about the same as WS pageviews.

I am not asking for an easy explanation for the differences. I am prepared to do the thinking for myself. But my problem is that I cannot find any details as to exactly how WordPress defines a pageviews/day. How for example does it handle bots? What is its definition of a day – UTC, local time? Are they unique pageviews in the GA sense, and if so how is a session defined? Can someone please point me to some authoritative source for this information?