DONALD TRUMP, the populist American president-elect, wants to deport undocumented immigrants. Podemos, the populist Spanish party, wants to give immigrants voting rights. Geert Wilders, the populist Dutch politician, wants to eliminate hate-speech laws. Jaroslaw Kaczynski, the populist Polish politician, pushed for a law making it illegal to use the phrase “Polish death camps”. Evo Morales, Bolivia’s populist president, has expanded indigenous farmers’ rights to grow coca. Rodrigo Duterte, the Philippines’ populist president, has ordered his police to execute suspected drug dealers. Populists may be militarists, pacifists, admirers of Che Guevara or of Ayn Rand; they may be tree-hugging pipeline opponents or drill-baby-drill climate-change deniers. What makes them all “populists”, and does the word actually mean anything?

Widespread use of the term “populism” dates to the 1890s, when America’s Populist movement pitted rural populations and the Democratic Party against the more urban Republicans. (It was also used to refer to Russia’s 19th-century narodnichestvo movement, which largely comprised self-hating intellectuals with a crush on the peasantry.) In the 1950s academics and journalists began applying it more broadly to describe everything from fascist and communist movements in Europe to America’s anti-communist McCarthyites and Argentina’s Peronistas. As Benjamin Moffitt explains in his book “The Global Rise of Populism”, a conference at the London School of Economics in 1967 agreed that the term, while useful, was too mushy to be tied down to a single description. Some scholars linked it to frustration over declines in status or welfare, some to nationalist nostalgia. Others saw it as more of a political strategy in which a charismatic leader appeals to the masses while sweeping aside institutions (though not all populist movements have such a leader). Despite its fuzziness, the term’s use has grown.

In 2004 Cas Mudde, a political scientist at the University of Georgia, offered a definition that has become increasingly influential. In his view populism is a “thin ideology”, one that merely sets up a framework: that of a pure people versus a corrupt elite. (He contrasts it with pluralism, which accepts the legitimacy of many different groups.) This thin ideology can be attached to all sorts of “thick” ideologies with more moving parts, such as socialism, nationalism, anti-imperialism or racism, in order to explain the world and justify specific agendas. Poland’s Mr Kaczynski, a religious-nationalist populist, pushes for a Catholic takeover of his country’s institutions from elite secular liberals. The Dutch Mr Wilders, a secular-nationalist populist, demands a crackdown on Islam (in defence of gay rights) and reviles the multicultural elite. Spain’s Podemos, an anarchist-socialist populist party, pushes to seize vacant buildings owned by banks and distribute them to the poor, and attacks “la casta” (the elite caste).

This “thin ideology” definition of populism seems apt in Britain, where Brexiteers denounce experts, refer to themselves as “the people” and boast of having “smashed the elite”. Indeed, Brexit seems to lack a unified “thick ideology”: Brexiteers have different attitudes to trade, race, government spending and almost everything else. But other scholars feel that the thin-ideology definition fails to capture some dimensions. Jan-Werner Müller, a political scientist at Princeton University, thinks populists are defined by their claim that they alone represent the people, and that all others are illegitimate. And there are important distinctions within the category, such as that between inclusive and exclusive varieties. Exclusive populism focuses on shutting out stigmatised groups (refugees, Roma), and is more common in Europe. Inclusive populism demands that politics be opened up to stigmatised groups (the poor, minorities), and is more common in Latin America. Mr Mudde argues that while most writers deplore populism, its upside lies in forcing elites to discuss issues they prefer to ignore. But populism’s belief that the people are always right is bad news for two elements of liberal democracy: the rights of minorities and the rule of law.