Definition - What does Dark Social mean?
The prevalence of sharing through dark social suggests that social media marketing that fails to focus on the type and quality of content may be overlooking a huge portion of social sharing.
Techopedia explains Dark Social
In analyzing traffic to The Atlantic, a Web analytics firm dug into traffic that came without a referrer and split into two types: Those who came to the homepage or a topics page (such as http://www.theatlantic.com/politics), and those who landed on a specific article page. Then, they made the assumption that the latter must come from some sort of referral, because it's unlikely that readers were typing long, complicated URLs into their browser bars. Based on this assumption, they discovered that more than half of The Atlantic's social traffic came from untrackable sources, or dark social.
Madrigal also suggests that this has implications for users. While they've been led to believe that in using social media platforms such as Facebook they are giving up personal data in exchange for being part of the social aspect of the Web, the prevalence of dark social suggests that the Web is - and always has been - social, whether users communicate over Web-based social platforms, or use other technologies such as email or chat.