I define privacy as not disclosing PII. PII is defined by the Interactive Advertising Bureau (IAB)) as "information about a specific individual including name, address, telephone number, and email address — when used to identify a particular individual." I don't want you and especially not the government to be able to find my house after I anonymously post a controversial opinion about politics.
Knowing you at some level is not necessarily a violation of your privacy if it cannot be traced back to PII. For example, suppose I am a search engine and you type in the query "High performance tires". I know at that moment that you are interested in them. I might want to show you lots of ads for Pirelli, Michelin, etc. I know you at some level, but I don't need to know your PII.
It gets tricky though. Sometimes information which isn't directly PII can be used to infer PII. IP Address, GPS information, device identifiers, and others (even simple demographics) can sometimes be traced back to identity, especially when collated with registration information and government databases. The more indirect information you might have, the smaller the set of potential people who fit the data and the easier it would be to determine the identity of the person.
