Refers to a believer of Trotskyism, one of many offshoots of Marxism, established against Stalinism. Named for the intellectual Leon Trotsky, who advocated for - among many things - internationalism, soviet democratization, and decentralized economic planning. Trotskyists thus opposed containing socialism to one country, the massive bureaucracy of the Soviet Union at the time, and the anti-democratic current of the period.
Depending on who you ask, Trotskyists are either enemies of the working class or fundamentally no different from Stalinists. Looked down on by Tankies and capitalists alike.
Trotskyists claim to be to the left of Stalin and closer to "true" communism.