The term Progressive or Progressivism is used in two different ways.
Rebranding the Traditional Democratic Party
One use of the term Progressive is as a public relations and marketing effort to rebrand the traditional Democratic Party. The use of the word "progressive" communicates the message that the Democratic Party is not just in favor of policies that development and improve the United States but that it is taking action to implement those policies. It is designed to indicate movement in a positive direction. Those using the term in this way are unaware of the goals of those who are working to promote Progressivism within the Democratic Party. Essentially it is a misunderstanding of the goals of the Progressives.
Euphemism for Socialism
The main use of the term Progressive is as a euphemism for Socialism. The word Socialism has been considered a "dirty word" in mainstream politics, by both the Republican and Democratic Parties, as Socialism is antithetical to the American system of government (see Americanism). As an effort to promote Socialism through Incrementalism, some socialists have joined the Democratic Party and attempted to promote and implement Socialist policies through the Democratic Party, often using the term Progressive to describe their policies.
How to Tell the Difference?
In order to distinguish between the two uses of the term compare the policies being promoted by those using the term with basic American (see Americanism) principles and those outlined by known Socialists and Communists (example The Communist Manifesto).
If the policies are in line with basic Americanism then it is merely a term being used by Democrats whose goal is to rebrand the Democratic Party. If the policies are in line with Socialism and Communism then it is merely a euphemism for Socialism, Communism, or some other form of Leftism.
Traditional Democrats are not Socialists or Commuists. When Socialists, Communists, etc enter into politics they often attempt to operate from within the Democratic Party as there has not been enough support for open Socialists or Communists in the United States. The principles of Americanism are the opposite of Socialism and Communism and there is no way to have compromise between them. For example, you cannot have some free speech as opposed to all or no free speech. If you limit free speech to only speech in favor of certain "acceptible" viewpoints then you are left with no free speech at all as opposed to "some" free speech.