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

Undefined Page Linked From
18.5 Beta 2 Version News Page: What is New in MagicDraw 18.5 SP3 (MagicDraw 18.5)
Page: What's New in Cameo Business Modeler 18.5 SP3 (Cameo Business Modeler 18.5)
Accessing Event data Page: 19.0 Version News (Alf Plugin 18.5)
Accessing data in Activity Edge guards Page: 19.0 Version News (Alf Plugin 18.5)