If I simply went by many here on DU, a "true Progressive" is someone who is anti-corporate and very liberal. The truth is, trying to determine who and what constitutes a "true Progressive" is like the problem Conservatives have in trying to define the meaning of Conservatism.
According to Dictionary.com, a Progressive is,
1. favoring or advocating progress, change, improvement, or reform, as opposed to wishing to maintain things as they are, esp. in political matters: a progressive mayor.
2. making progress toward better conditions; employing or advocating more enlightened or liberal ideas, new or experimental methods, etc.: a progressive community.But it's not as simple as the definitions given above. Many people have labeled certain issues as being Progressive and if a particular politician doesn't feel the same way...they don't fit the mold so-to-speak. Case in point is the candidate I'm supporting for 2008, Barack Obama. I don't think anyone would argue that he's not a reformist. Him and Russ Feingold put through legislation that would have created an independent ethnics committee instead of what Obama calls simple bandages that aren't solving anything. He also has legislation on the table for Voters Rights that would make it criminal to mislead and intimidate voters. But, one of the staples on the "Progressive Movement" is being anti-globalization...and even though Obama didn't vote for CAFTA (he voted nay), by all intents and purposes...he's not anti-globalization.
http://obama.senate.gov/news/050630-why_i_oppose_cafta/index.html">Why I Oppose CAFTA -Barack Obama, 2005
Does this mean Obama is not Progressive? Does this mean he's a corporatist? No. It's like the theory of the "True Negro" (another problem Obama seems to be facing). I don't believe there is any group of stances that determines who is progressive and who isn't, just like there shouldn't be any group of physical traits that determines who is Black (ie. thick lips and kinky hair). You just have some people who are MORE Progressive than others, like if you compare Dennis Kucinich with Barack Obama. Both are Reformists, but one moreso than the other.
I also noticed people on this board got really upset when Barack Obama and other Dems didn't go and campaign for Ned Lamont...so he wasn't a "true Progressive." I think it's petty to hold people to a strict guideline of stances for such a loose term.