So while the Digital Advertising Alliance exits the DNT group stating a number of reasons including ill-defined scope, no definition of tracking etc, we're back to the same place and that is we have once again failed to define what privacy actually means.
We still do not have a good theory of privacy or even common terminological framework that uniﬁes the engineers, scientists, mathematicians, lawyers and consumer advocates - let alone the end user - yet.
Failure to define what DNT is (or was), the semantics of tracking and the very definition of what privacy is in this context was probably the major factor in the failure of DNT to progress and bring disparate groups with differing notions of privacy successfully together.
Indeed the above is just one symptom of the malaise that is affecting privacy and also in a wider scheme the very ideas of data processing and Big Data. We are not spending any time thinking about the semantics or meaning of these. Within the privacy community even trying to start a discussion on the semantics of privacy is fraught with difficulties that only Machiavelli and Kafka could have dreamt about.
From an earlier article entitled on the Naivety of Privacy I wrote:
I think we're missing the point what privacy really is and certainly we have little idea at this time how to effectively build information systems with inherent privacy  as a property of those systems. I have one initial conclusion:
WE HAVE NO UNDERLYING THEORY OF PRIVACY
We have no common definitions, common language, common semantics nor mappings between our individual worlds: legal, advocacy and engineering. Worse, in each of these worlds terminology and semantics are not always so well internally defined.
Maybe, the current difficulties of the DNT group will force us to reassess what we mean by "privacy" and "tracking"?