Understanding Feedburner Statistics

I am trying to understand the Feedburner Statistics widget. After installing Pwiki, it said…

Circulation 3156 3431
Hits 17795 17544
Reach 15 13

That seemed pretty steep considering I just got it started. Can someone explain these metrics to me?

Also, where does Pwiki get its data from? Is it from the code we insert into our html files? Raw Apache logs? If the former, does that code have to be on every page?

the stats are for the Piwik feed, you can put your feedburner login in the input box to get your own stats.

Can you explain this. Do you mean data from stats are being fed from my site to piwik ?

If so can I switch it off and how