Populist is a meaningless term that could be used to describe everyone from George Wallace to Bernie Sanders.
That doesn't mean it's meaningless. Merriam-Webster defines "populist" as "a member of a political party claiming to represent the common people" and then goes on to define the actual Populist Party of the late Nineteenth Century. It then gives a second definition as "a believer in the rights, wisdom or virtues of the common people."
Populist economic policies are, IMO, policies that look to even the playing field (which a populist would inherently see as unequal and/or unfair) for this "common man." The flaw of populism, from a "conservative" (gotta include my Santender trolling insurance 
) stance is that the definition of who this *common man* is, and whether or not the playing field is "unfair" is entirely subjective ... not to mention there will be incredible debate about how to level the playing field.
Put simply in our modern day context, I would say economic populism is undeniably tied to forms of redistributionism, be that higher taxes on the wealthy (to redistribute income to those who a populist believes deserves some of this money more), more regulation on business (to redistribute profits to smaller employers and/or consumers who "should" be getting more of that money), trade restrictions (to level the allegedly unfair dynamic of free trade in favor of the industries that aren't benefiting "enough" from it) or other policy measures that look to achieve the same redistributionist goals. I think economic populism fundamentally has to draw on the rhetoric, style and sometimes the specific policies of the tradition of Jeffersonian and Jacksonian egalitarianism that sought to be a "check" on "monied interests" and other economic "elites." Cultural or social "populism" would, of course, be different, but I don't see how economic populism can be explained without a clear and precise tie to some form of redistributionist sentiment.
Not really, as darklordoftech pointed out, populism is really about setting up an amorphously defined "people" against, not necessarily an elite, but against an enemy, or out group, who are blamed for exploiting or taking advantage of the "people" as a whole.
That is why you have, for example, rhetoric about welfare scroungers as a form of populism, but one which is manifestly not redistributive in nature.
