The term is used both politically and descriptively. When it is used politically, it is done to stigmatize someone. Effectively, it's an insult that people believe to be appropriate.
A good comparison would be the word "pedophile." It is also a word which can be used descriptively and which can be used as an insult towards those who don't fit the precise definition of the word.
The stigmatizing sense of the word, of course, works because the people who do fit the description tend to be remembered with disgust. So the words are effective at expressing the notion of disgust.
The logical question is what is the "descriptive" use of the word "fascist"?
Well, it was coined by Mussolini, so describing what Mussolini meant by it is a good start.
It's main components are
- nationalism
- irredentism (desire to restore, usually by military mean, territory lost in conflicts which have since been settled) and expansionism
- corporotism that goes beyond merely a state protecting corporate interests, but goes as far merging of corporate and public functions
- racism as state policy, not necessarily of suppression, but as a social pecking order; not necessarily outright antisemitism (by many accounts Mussolini was not antisemitic and was generally reluctant to oblige Hitler's demands for participation in the Holocaust activities)
- totalitarianism
- opposition to classical liberalism with the view on it as a hyper-individualism which must be suppressed for the benefit of the abstract state
Also while it hasn't been described as an essential part of the Fascist doctrine, another element which is traditionally present in Fascist states is multiple competing security forces which ensure loyalty through extra-legal repressions.
For example, I've argued in a different answer on this site that the social order in the modern Russian Federation is best described as "Classical Fascism."
I was recently surprised to see that Timothy Snyder, a Yale history professor, who researches Eastern Europe, has written the following:
if Russia today is not a fascist regime, it is really difficult to know what regime would be fascist. It is more clearly fascist than Mussolini's Italy, which invented the term.
And while you can mis-attribute my opinion to the ease with which anonymous internet accounts use foul language, the same cavalier attitude is generally not observed among the Ivy League professors.