All the answers and comments here appear to be echos of each other, using the question as an excuse to make claims everyone on the right is bad and no-one bad exists on the left. They seem to all hinge upon using the fact there are not so many hits on google due to the leftward media bias or that the extreme-right embraced their moniker as 'evidence' for these claims. While in fact just as manyMany people on both sides falsely label their opponents.
The fact is there are bad on both sides and the simplest answer to the stated question is
Alt-left is the name given by conservative groups to the most extreme members of the left
Just as alt-right is used to describe the extreme elements of the right. (including, as state in other answers, by those extreme-right wingers themselves). So there is no real difference in labeling them far-left or alt-left.
Most commonly it is used as a term to denounce groups and individuals committing violent crimes (notably antifa and various individuals on university campuses) and those who use fraud to progress their agenda (fake hate crimes) and who push for false equality and affirmative action (I'm more equal than you)
I'm new here, but I've read a lot so I know how it works - don't forget to vote based on your own biases and emotion rather than content (thumbsup)
