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][1] or that the extreme-right embraced their moniker as '*evidence*' for these claims. While in fact just as many on both sides [falsely label][2] their opponents.

The fact is there are [bad on both sides][3] 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][4] [crimes][5] (notably [antifa][6] and various [individuals][7] on university campuses) and those who use fraud to progress their agenda ([fake hate crimes][8]) and who push for [false][9] [equality][10] and [affirmative action][11] (I'm more equal than you)


  [1]: http://www.washingtontimes.com/news/2017/mar/26/media-bias-leans-left/
  [2]: http://www.breitbart.com/milo/2017/02/14/politico-falsely-labels-milo-alt-right-journalist/
  [3]: http://markhumphrys.com/left.right.violence.html
  [4]: http://www.dailywire.com/news/10664/video-trump-voter-dragged-his-car-and-beaten-gang-chase-stephens#exit-modal
  [5]: https://www.thesun.co.uk/news/1836515/shocking-footage-shows-white-man-begging-rioters-for-mercy-while-being-beaten-as-a-reporter-is-nearly-dragged-into-a-fire/
  [6]: https://www.washingtonpost.com/news/morning-mix/wp/2017/08/28/black-clad-antifa-attack-right-wing-demonstrators-in-berkeley/?utm_term=.e5b7a0ebd17e
  [7]: http://www.foxnews.com/us/2017/10/06/uc-student-who-stole-maga-hat-in-viral-video-could-face-felony-charges.html
  [8]: http://www.fakehatecrimes.org/
  [9]: https://aclu-co.org/court-rules-bakery-illegally-discriminated-against-gay-couple/
  [10]: https://milo.yiannopoulos.net/2016/10/bartender-refuses-trump-supporters/
  [11]: https://www.theguardian.com/world/2017/aug/04/affirmative-action-california-black-hispanic-students