There's no single definition for the term.
Populism often refers to a politician or influential figure that focus on the people. But it can also be used to refer to someone to defend "most people" as in, a majority. The term is also used in developed countries to refer to figures that protected the worker's class and in under developed countries, they use the term populist to refer to left leaning politicians who promise to help the poor.
The populists of the late 1800s were generally farmers. Since big business were emerging in the country, most likely, a populist would stand up to defend the majority of the population and their source of income, which was farming.
But in 1830 we have Andrew Jackson as a populist figure. Also, a different kind of populist. He wasn't about "spreading the wealth". He was against the State interfering too much in basically anything. He was even against the government building roads and canals.
Also, Jackson ended the central bank and paid off the national debt.
In order to "protect the little guy", Jackson believed that we should diminish the government's power as much as possible, since its interference in the economy would only help those with power to buy that interference.
According to Jackson, by allowing the government to have that much power would only increase the amount of advantages that it would give to those that are closest to it.
Jackson's arguments have a solid foundation if you consider that the Republican Party, that fought and won the Civil War, sponsored aid for railroads and favored corporations. In the end, the party was caught up in a series of scandals that supported Andrew Jackson's views about this subject and even today, Jackson's ideas are defended by classic liberals and libertarians.
