Dark social refers to social sharing of content that occurs outside of traditional social media networks and web analytics, such as sharing links via email or messaging apps. It is difficult to measure this type of sharing as it does not occur publicly on social networks. While tools like Tynt or Rio SEO can provide some measurement of dark social sharing, one cannot fully track this hidden web traffic with standard analytics. The best approach is to acknowledge dark social's existence and measure as much of it as possible.