Okay, I think I already know, but I want to make sure, and this surprisingly simple question was surprisingly hard to google. :P
In the tomcat manager, I have some session stats, like so:
Active sessions: 1 Session count: 1 Max active sessions: 1 Rejected session creations: 0 Expired sessions: 0 Longest session alive time: 0 s Average session alive time: 0 s Processing time: 0 ms
Is session count just the number of sessions created since the server started?
Session count is the number of current users online.
After an user leave the site the session can remain alive for next x minutes until expire.
Depend of what your reporting tool does, Active sessions may be the number of sessions that registered activity from users on the last 5 minutes.
Edit: the Expired sessions may be the number of all sessions created and expired since the server started
Active sessions: The number of currently active sessions (not expired)
Session count: The total number of sessions created since the server started.
Expired sessions: Session count - Active sessions