This report shows how many recipients have asked to be removed from your address book(s) by clicking on the unsubscribe link in your email.
This also includes those recipients who have reached their bounce threshold (as set under Contacts > Suppressed contacts > Bounce settings) and those who have used Hotmail/MSN, AOL and Yahoo's 'This is junk' functions.
These addresses are automatically removed from your address book(s) so that they can't be emailed in the future. This would apply even if these email addresses were included in a future upload to the same or different address books. They'd be automatically excluded from the upload.
A complete list of all addresses removed can be found under Contacts > Suppressed contacts.
Using the report
The report will display all of the recipients who've unsubscribed, along with the date and time that they unsubscribed.
Clicking on the Display button will enable you to change the view of this report.
Clicking on Export next to it will provide options to either export the contacts list into a CSV file or create a new address book with them.
To view the drill down detail on other reports, use the More reports... (located next to the title of the report). This will provide a menu from which you can select the report type, as shown below.