Will someone PLEASE explain to me what these "ANTIFA's" are you're talking about!

One word keeps coming up in this Charlottesville attack that I can't make heads or tails of.

What The Fuck is an Antifa?

If it means anti-fascists then I'm a fucking ANTIFA!  I'm gonna assume that people aren't stupid enough to support fascists on my page (although many are coming so close it really doesn't matter) so if it isn't as is said on the internet as being anti-fascists then what the fuck is it!

What is the meaning that you people are associating with the term "ANTIFA"!