Far Left is a term used to describe political ideology on the far left side of the Political spectrum. The primary ideologies seen at this end include Communism, more extreme forms of Socialism, and Anarchy.
According to the Nolan chart, the farthest left-wing ideology would be Anarcho-communism, combining maximum social freedom with total economic equality. If an anarcho-communist society in modern times existed, it would have the potential to be an excellent society. Everyone would be equal, everyone would have their basic needs satisfied, and there would be a very high amount of personal freedom.
So-called "Far Leftists" that have done evil things are Stalin, Mao, Kim Jong Ill of North Korea They have no connection to Liberalism or Democratic Socialism or Social Democracy. However, it is dubious if they should truly be called far left. If anything, they would be considered right wing on the axis of personal freedom on the Nolan chart. They would also be considered right-wing economically, if the left-right economic line is meant to be the spectrum from inequality to egalitarianism. Their societies had low personal freedom, along with strong social hierarchies based around the dictator.
While these ideologies are superficially left wing, they often end up turning into dictatorships and other things of that nature, which is why they're given their own article, rather than be seen as part of the regular left wing. Therefore, they're no longer true to liberalism, either. A true left-winger believes in peace, tries to prevent war, and pro-gun control, to name some examples.
It's sometimes difficult to see any difference between the far right and the far left. The state controlled Socialist system in Communist countries has much in common with extreme monopoly Capitalism since the state controls the whole economy. However the USSR was never Socialist it was Communist so we hope all those right wingers will notice, there's a difference.