Good question. Unfortunately, I doubt that any leftist will be able to define it for you, ergo why that term is included in my 'Lispy Leftist List of Linguistic Lunacy'. As far as I can gather, anyone who isn't a part of their leftist hive mind is a part of the "extreme right", whatever THAT means.
Since I am a supporter of the MAGA movement (currently spearheaded by Donald J. Trump), I have been referred to as various things, including but most certainly not limited to:
** Deplorable (Hillary Clinton)
** Listless Vessel (Ron DeSantis)
** Ultra MAGA (Joe Biden and/or his handlers)
** Cult member needing "deprogramming" (Hillary Clinton)
** Far-right extremist (leftists in general)
** Conspiracy theorist (leftists in general)
** Bible thumper (leftists in general)
** Threat to "democracy" (leftists in general)
** Racist, Bigot, Homophobe, Xenophobe, Misogynist, et al. (leftists in general)
** Domestic terrorist (Intelligence Branch of the SODC)
Agreed