It originally was used to describe Leftists supporting authoritarianism while claiming to be leftist. It was used originally to describe Marxist-Leninist members of the Communist Great Party in Britain who supported the use of tanks by Soviets to quell a couple of uprisings in the late 50s and late 70s. It has since evolved as a term since then to include Leftists (or maybe not even leftists anymore, it's getting thrown around a lot now) who support similar actions in China and Russia. Usually they have an obsession with Mao and/or Stalin and China can do no wrong in their mind while claiming the western world is evil.

The term has an interesting history (to me as I'd describe myself as leftist, but I look at is as we all suck and can all improve) and Wikipedia has a decent article on it that I pulled most of this info from to double check my memory. Unfortunately they tend to be the most vocal part of leftist communities so I just tend to ignore any of them...