It is important to understand that the statistics are for the current book search results. So if you want the statistics for the full database, make sure you do a full database search or select the Search->All Books menu item.
Number of titles (records) - This is the number of different titles displayed, i.e. the number of records.
Number of books - This is the number of books displayed. The difference between the title and book counts is that books include copies. So if you have 2 books displayed and 3 copies of each book, the title count will be 2 and the book count will be 6.
Number of Volumes - This is the number of volumes. i.e. it includes volumes in a multi-volume set.
Number of Active Loans - The number of books that are currently out on loan.
Number of overdue books - The number of books that are currently overdue.
Number of books never checked out - The number of books that have never been checked out. This can be used to determine which books are unpopular.