"Dark money" refers to political spending where the ultimate donor is shielded from public view. The most common channel is the 501(c)(4) social-welfare nonprofit, which can spend on issue advocacy and political activity (so long as politics isn't its "primary" purpose) without disclosing donors. LLCs and trusts can also be used to route money into Super PACs while obscuring origin.
Dark-money spending exceeded $1 billion across recent presidential cycles, on both left and right. Disclosure proposals — DISCLOSE Act variants, FEC rule changes, IRS reforms — have so far stalled.
Defenders argue donor anonymity protects free association and shields donors from harassment; critics argue voters cannot evaluate political speech without knowing who paid for it.