I wouldn’t say this citation is Privacy Guides’ definition of privacy, rather an explanation of privacy in contrast to security and anonymity in the context of the digital world (link to citation). Privacy is about more than data protection but also information in a general sense, and also encompasses non-interference for instance seclusion and bodily integrity.
Consent and security are fundamental to maintaining privacy. In that sense, no matter how many times people say “that’s privacy, not security” (or vice-versa), or “privacy vs. security” (this needs clarification: security for who?), privacy and security are inseparable while being distinct.
I think this Wikipedia definition works well enough so I’ll post it here.
Privacy is the ability of an individual or group to seclude themselves or information about themselves, and thereby express themselves selectively.
As others have posted, what information someone shall reveal about themselves depends on a range of factors including goals, threats, vulnerabilities, capabilities etc. Privacy is about choice, not secrecy for the sake of it, and it’s a very individual choice. The privacy advocates who show their face and real name perhaps believe they will achieve more by doing so and are less concerned about their face and name being used against them. Other people may expose themselves to unacceptable risks just by showing their face and name.
OP @SYST3M_D3STR0YER may be shocked at the amount of data people post about themselves compared to 20 years ago. I wonder how this has evolved over time from the early 2000s to now. When I first used the internet there was awareness of being careful about posting personal information and interacting with other people online that I feel exists far less today.