Activist political slang, short for anti-fascist. Probably German in origin (it's the widely-used abbreviation for the German AFA group), it refers especially to militant anti-fascists who engage in physical confrontations with Nazis, such as members of Anti-Fascist Action (AFA).

A terrorist group generally made up of degenerate anarchy loving teenagers, similar to that of the ARA, who hate anyone that is a racist/nationalist/"nazi"/etc.
They are well known for not being able to hold any sort of protest or demonstration without becoming rowdy, damaging property, or attempting to use violence.

Antifa is a group of skinheads generally made up mixed color/culture and consist of mainly White, (biracial Black/white), Jew, and South American. Antifa's view life as a struggle, that needs to be fought through; against the racist/Neo Nazi, white supremacy, racist-Skinheads. They are well known for not being able to hold any sort of protest or demonstration without becoming rowdy, damaging property, or attempting to use violence. Antifa’s engage in physical confrontations with Nazis, such as members of Anti-Fascist Action (AFA). Although Antifa are considered Skinheads; they do not participate in racist activities. Antifa’s believe it has more meaning to fight with the strength of the body and using your fist opposed to using weapons.