Who is a fascist? Nowadays political opponents call each other "fascists" all the time but I have no actual idea what this means.

We are speaking very broadly here, but I will do my best to give you a good answer to your question. The FAQ posted by the Moderator will be very useful, I hope that my answer is useful to you as well.

Fascism is a far-right, ultranationalist political ideology created by far-right conservatives disillusioned with liberal democracy after World War I. The two most memorable fascist rulers were indeed Benito Mussolini in Italy, and Adolf Hitler in Germany, who's "National Socialism" is really just considered the German interpretation of fascism. The majority of scholarship also considers Francisco Franco's "National Conservatism" of Spain to be the Spanish interpretation of fascism as well. As you can already see, what makes a government "fascist" is not what they call themselves, but how they act. There will always be debate among historians when it comes to the application of labels, especially labels for political ideologies, to governments. But I do not plan to mention any government that is not, by a great majority of scholarship, considered fascist.

Fascism rose after World War I in Italy and Germany due to a growing discontent among the far-right with liberal democracy. Fascists opposed the representative governments in favor of totalitarian, one-party states. They were strong militarists and imperialists, both Italy and Germany had grand plans to annex a greater portion of the world than they had previously. They are ultranationalists, the promotion of the importance of their state, which they believed was representative of their nation, above and at the expense of everybody else. This belief supported Nazi Germany's actions in the holocaust, and fascism's close ties with racism. They are social traditionalists, fascism is a deeply socially conservative ideology that opposes every facet of progressivism. They were very strong on the gender roles of men and women in their society and expected men and women to adhere to them strictly.

Economics is an important thing to talk about here and fascists had a very strange relationship with it, and there is variance from country to country that makes it hard to pin down exactly what makes a fascist economy a *fascist economy* to the finest detail. This is also where the confusion of National "Socialism" enters the fold. Fascists opposed both economic socialism and the liberal free-market capitalism, the economy belonged to the state, the representative of the nation. Fascist governments supported the notion of private property, contrary to some popular belief they did not nationalize it; in practice, fascism never really opposed the class system of capitalism, instead they simply made it more rigid by directly enforcing it with the state as their tool. The only aspect of capitalism that fascists can be said to consistently dislike is the free-market.

You may, like most other people in the world, be wondering why the Nazi party called themselves "National Socialists" if they openly opposed economic socialism and were far-right social conservatives. National Socialists co-opted a large amount of Marxist/socialist terminology in order to appeal to those very same leftists. Instead of socialism based on economic class, the traditional definition, it was nationalist "socialism" based around national identity. They did not support economic socialism, Marxism, or leftism, they only supported that spirit of unity that socialism inspires but applied it to national identity and used it to further their nationalist agenda. I recommend you read more on your own about the Nazis co-opting leftist terminology, because that could be its own post so I do not want to spend too much time on that.

Now, more directly to the point of your question, I am going to discuss how fascism is represented today. This is less historical, but very important because there is a lot of debate about whether referring to anybody after the year 1945 as a "fascist" is correct or not, because technically the historical conditions that created fascism in the first place cannot be recreated. However, generally speaking, most scholarship would agree that the most extreme views of the far-right are well represented by the fascist ideology. In the start, we mentioned Hitler, Mussolini, and Franco; I am also going to throw Imperial Japan into the ring here, while I am not a scholar of Japan, I am aware that there is not much debate that the political ideology of World War II Japan aligned closely with fascism. These four are the most seldom debated interpretations of fascism. When trying to determine if a government, even in modern times, aligns closely with fascism, you need to take a look at the policies of the government to see if they resemble the actions taken by fascist governments. This could be a conglomerate of the tenets that I outlined earlier. Considering we still live in a political climate where socialism is the left-wing, liberalism represents roughly the center or center-right, and fascism represents the far-right, it is indeed possible for people today to align with fascism. However, for them to be a fascist, they should show support of some of those very same tenets. If they are in favor of a one-party state but support nationalization of the means of production and social progressivism, they are more likely a communist, for example. Fascism is a conglomeration of extreme right-wing viewpoints, and several of them have to be met for our subject to be considered fascist rather than a conservative, a liberal, or anything else.

An FAQ was commented while I was working on this, so they have further reading, but I have two writings here that you can take a look at, both are useful reads in understanding fascism. One from a fascist himself, and one from a communist who opposed fascism:

The Doctrine of Fascism (1939) - Benito Mussolini

Fascism: What It Is and How to Fight It (1944) - Leon Trotsky

Edit: tried to fix some formatting