An 'undefined' page is any page that has been linked to from within Confluence, but that does not yet exist.

Undefined Page Linked From
Creating TSIG Page: Configuring TSIG Keys (BloxOne DDI)
Deleting TSIG Page: Configuring TSIG Keys (BloxOne DDI)
Modifying TSIG Page: Configuring TSIG Keys (BloxOne DDI)