There isn't really any sharply defined definition of fascism, but to know what it is I think you have to look at its historical origin. I think the Roman etymology of the word is a good symbol of fascist ideology, the fascia, which is a binding of a bundle of sticks, and relates to that old metaphor that a single stick is easy to break but a bundle is unbreakable. Fascism requires the subordination of the individual for the good of the state, and the interests of the state is the highest value in fascist ideology. That is not the same thing as some generic dictatorship like some latin american military junta, although fascist states tend to be dictatorships.
TLSguy has made the argument in the past that fascism can somehow be leftist, but that is impossible and contradictory. Of course, leftist ideologies can degenerate into dictatorships, but it there are some important distinctions. Leftist political philosophies are more concerned with all mankind and reject nationalism in favor of internationalism. Leftist philosophy also is more concerned about the welfare of the individual, and that ultimately the state should have the welfare of people as its priority rather than people serving the state. Simply put, fascism is tribalist, and leftism is individualist. Fascism is exclusively a right-wing political philosophy.
Obviously a lot has been written about fascism, and many people have attempted to define it, but I think one of the most insightful and best pieces on the subject was written by Umberto Eco in
this essay for the New York Review of Books. That is a deep dive into the subject, but if you want something more concise,
here is a checklist of traits fascist ideologies.
