Portmanteau of "Viacom" and "Communism".
Any act of, or belief system held by, a company (especially Viacom) that involves removing, suspending/suing the publishing account of, and/or blocking (usually to everywhere except the USA) videos containing anything made by the company or one of its subsidiary companies. Very common on YouTube. Extremely frowned upon and often incites boycotts and/or outrage videos.
Term coined independently and almost simultaneously by several YouTube users after Viacom became infamous for this practice.