Where can I find description of Admin Stats numbers?

Question

I'm particularly interested in the last section:

For what time frame do these numbers apply? 

I've tracked history over the past month or so, and I see that on 1 Nov, we had 48,846 active users. Today, as shown above, we have 49,799.

Is that 49,799 active users for the moment in time that I checked the stats? When will this update?

Also, what do the numbers in the Categories section represent? Do they show the number of posts per category? Are only the main posts being counted but not the responses to them?

If there's a help page for all of this, a link to that would be great! Thanks! 

Comments

I believe "active users" is a misleading label. It may be the number of users who registered (or may be those who registered and confirmed their emails). If you don't have any anti-spam tool, those "active users" are mostly spammers. Maybe it's not your case. The numbers in brackets after category names in Category widget are the numbers of questions. Answers and comments are not counted.