Liberalism in itself doesn't have a clear social/political definition.
Fixed it for ya.
Yes, I know, you can quote this or that authoritative source to refute the claim. And the refutation will have a very simple counter-refutation.
One country's "Liberal" party is "left wing", another's is "right wing", and still another's is "centrist".
This may not make sense from an Americentric position (and this seems to apply to "both sides" of Americentrism), but then that's also the point -- the search for a clear, standard definition is problematic, because politics around the world is just too complex a subject.
You have your classical liberals and your neoliberals and your liberal socialists and so on, so why not classical populists etc.?
Then you can tell people with pride that you're not one of those populists. You're in a good denomination.
But the problem with liberalism is not liberalism itself (same applied for libertarianism), it's people who claim to be liberals and then promote social and economical ideals in line with Marxism and communism.
We can fix that too.
But the problem with populism is not populism itself (same applies to humanism), it's people who claim to be populists and then promote ________ and ________ ideals in line with ________ and ________.
You can use the same formula for any -ism.