Left wing person who defends authoritarian regimes.

The term comes from when the Soviet Union rolled tanks into Budapest in 1956 to crush the Hungarian revolution, which aimed to end bureaucratic despotism and place power with the workers. Many Western communists were horrified by the slaughter, but some supported what happened & continued to back the USSR.

Today "tankies" tends to refer to people who support China & Russia, and sometimes even North Korea & Iran, often because they take the view that anti-Western == good, ignoring that these are highly oppressive, exploitative regimes which have nothing in common with typical left wing values.

Some are just naïve about the reality of these governments, others just think of it as an "enemy of my enemy" utility against neoliberalism & Western imperialism, but some seem attracted by the idea of being authoritarian themselves or believe that a left wing future can only be achieved & maintained through authoritarianism.

Online, it is probable that some tankies are working for China or Russia and that others are working for Western organisations seeking to disrupt & discredit left wing movements. Others have just been persuaded by tankie arguments.

As a caveat: sometimes "tankie" is used to describe left wingers who aren't like those described above, but who prefer the idea of imposing socialist reforms through force with a vanguard party at the helm, over achieving reform through anarchist organising without hierarchical enforcement.