With full respect to the author I do believe that the self of typical software beta can be compared with a human being’s self.
Public: A common set of features that are visible to both my market and myself.
e.g. – I am a project-management system. Everyone knows that I offer excellent flexibility in a collaborative environment and assist teams in priority assignment of tasks.
Hidden: Set of features which only I know but my market i.e. my target audience/prospective customers do not know.
e.g. – While I know that I can be integrated as a plugin to many IDEs not many in my market are aware of that.
Blind: Things which are known to my market but I am myself unaware of them.
e.g. – Cross-functional teams find me very easy to use. I am unaware of it because I belong to the other side of the coin. My market helps me discover these features.
Undiscovered: It is the zeal to achieve this. Set of attributes, properties, features which neither me or my market not. Hidden/unknown to everyone.