The political style and ideology that pits a virtuous people against a corrupt elite — a form of politics that has appeared across the left-right spectrum, in democratic and authoritarian contexts, and in every region of the world — and one of the most contested concepts in contemporary political science, not least because it is simultaneously a diagnosis of democratic dysfunction and its symptom.
Populism is the accusation that democracy's enemies always make against democracy's defenders — and the accusation that democracy's defenders always make against its enemies. Donald Trump called himself a populist and was called one by his opponents. Hugo Chávez called himself a populist. So did Bernie Sanders, Marine Le Pen, Narendra Modi, and Jair Bolsonaro. A concept that describes both left-wing and right-wing movements, both democratic and authoritarian leaders, both the 19th-century American farmers' movement and the 21st-century European far right, must either be capturing something real that crosses these divides or it must be too broad to be analytically useful. The answer, as with most things in political science, is: both.