A false flag operation was a hostile action in which the perpetrator attempted to disguise themselves in order to frame another party.
In 2154, the Romulan Star Empire sought to sow conflict between their adversaries by launching a series of attacks on Humans, Andorians, Tellarites, and other powers, using drone ships that could masquerade as a different vessel via multispectral emitters. (ENT: "Babel One", "United", "The Aenar")
In 2259, the Broken Circle mining syndicate on Cajitar IV attempted to launch a false flag operation on the Klingon Empires using a false Federation starship, NCC-1279. Their goal was to reignite the Federation-Klingon War. (SNW: "The Broken Circle")