On the left is the number of unread and on the right is the total number in that folder. It depends on what view you are using whether it is indicating messages or conversations. The folder properties always shows the number of messages, never the number of conversations.
This is all different in the Upcoming version 10. We now have the search box in the title bar, and no other information there. In that version we show the read/unread count on mouseover:
