PostEaseThe short answer
Dark social refers to content sharing that happens through private, unmeasurable channels: a link sent in a DM, a screenshot texted to a friend, a post shared over email. That is the opposite of sharing that leaves a visible, trackable trail, like a public repost. Analytics tools cannot see or attribute it, hence "dark."
Why it matters even though it cannot be measured directly
A private recommendation from a friend often carries more trust and influence than a public share, precisely because it feels more personal and less like marketing. Dark social is frequently where the most persuasive sharing happens, even though it never shows up in a platform's own analytics.
An indirect way to notice it
A sudden spike in direct or unattributed traffic to a website, with no corresponding spike in public shares or trackable referrals, is often a sign that dark social sharing is happening. The signal is indirect, since the sharing itself cannot be tracked, but it is a real one worth watching for.