This is how many days you have left before your character is automatically deleted if you don't login. The counter is reset to 30 every time you login. So basically if you don't login for 30 days then your character would be deleted. Unless you are a VIP as they are exempt from this. If your interested in becoming one check out the upgrade store of the right for more info.
Note: You may also place your character in Vacation Mode which will save your character from deletion for 90 days. Once you log back in it resets to 30 so once you set it don't log back in until your back. Deleted accounts are not restored.