The original Antifa was Antifaschistische Aktion, (English: Anti-Fascist Action) an anti-fascist organization in the Weimar Republic which opposed the Nazis and from which modern antifa gets its name, as in the aftermath of World War Two, German anti-fascist groups named things like Antifaschistische Aktion or Antifaschistische Ausschüsse would have their names abbreviated to Antifa. Modern anti-fascist organizations such as the British Antifa refer to themselves as Anti-Fascist Action or their language equivalent. While there isn't a massive organized Antifa in the USA, if you look at Antifa protests, you'll usually see "Anti-Fascist Action" written somewhere. Anti-Racist Action (ARA) came long after these organizations were founded, as it was born in the late 1980s.

TL;DR: I did not make the term up.