The Biden DHS called them “loosely affiliated organizations” because they were underground. Closest analogy might be anonymous or lulz. You can see members show up to protests and carry Antifa flags, in full military gear, causing violence, etc. There are arrest videos on YouTube, and the ATF, DHS, and Florida AG went after some named members back in 2023

http://www.myfloridalegal.com/newsrelease/action-against-ant...

Also others have linked to other orgs later in this comments