On this tab, you can see a list of all users whose friendship you rejected. Once in the rejected status, the user can't request your friendship anymore. You can either Approve () some user's friendship, which makes them your friend, or Remove () the user from the list of rejected, which enables them to request your friendship again. By checking some of the check-boxes and clicking one of the Approve all selected friends or Remove all selected friends, you can approve or remove more users at once.
Detailed information about the Friends module can be found in Developer's Guide -> Modules -> Friends.