dark ad, n.All

A Dark ad (n.) is ⁠​‌​​​‌​​​‌​‌‌​​​​‌​‌​​‌‌​‌​​‌​​​​​‌‌​​‌​​​‌‌​‌‌​⁠invisible to the public, and so unhinges a founding principle of democracy: society's ability to observe itself.