I feel like it's a very ill-defined term in the imperial core, but also there seems to be no coherent agreement on the left. Many thinkers have different definitions that often overlap.
Lenin called fascism "capitalism in decay"
Fanon called it "colonialism at home"
Umberto Eco offers his own incoherent mess of a definition
Roger Griffin defines it as a "palingenetic ultranationalism" that imagine a mythical "rebirth" of some previous glory (Rome, the volk, MAGA), and in doing so seek the "dominance of the insiders of the ultra-nation over those outside of it."
Parenti states that fascism "offers a beguiling mix of revolutionary-sounding mass appeals and reactionary class politics", adding that if fascism means anything "it means all-out government support for business and severe repression of anti-business, pro- labour forces."
Andreas Malm adapts Griffin's definition in White Skin, Black Fuel to a "palindefenIve, palingenetic ultranationalism", etc, adding that in addition to the sense of rebirth to some mythical glory time, there is also a mythical defense of the ultra-nation from those who are defined as foreign, be they Muslims, central American refugees, judeo-bolsheviks, etc.
I find the most functionally useful definition of fascism is Parenti's: the violent oppression of the left to maintain the dominance of the ownership class. However I feel like it lacks the element of violent chauvinism against arbitrarily defined others in society. That is to say I suppose I also lack a coherent definition.
What say you comrades?
Everyone seems to agree that they define fascism as a mixture of two of the definitions listed in this post which I think reflects that there are two aspects to fascism, yes this is indeed a base-superstructure moment. The Base is the comically evil economic policy of protectorate capitalism and primitive accumulation (I'm sure you can identify more). The Superstructure is the crackpot ideology of the existence of a subservient class whose whole purpose is to serve the "greater" and the threat of the "barbaric" other, all of which is cooked up to justify the base. One of the reasons fascism is so confusing is because it is hard to separate from capitalism, the classes have a virtually identical character and their organization has not changed, only the exploitation has intensified. But eh, what do I know.
Not to mention the blatantly obvious, that it is an ideology created and perpetuated by history's biggest morons