Progressivism started as a social movement in the late 19th and early 20th centuries, eventually becoming a political movement. Teddy Roosevelt actually spearheaded the cause after taking office in 1901, mixing this with GOP conservatism. He said most everyone wants some progress but both Republicans and Democrats were slow to actually implement it. Roosevelt took it a step farther declaring he "always believed that wise progressivism and wise conservatism go hand in hand." Progressivism was highlighted in the Industrial Revolution, later when technology completely changed the way we do business. It was recently in 2014 that Andrew Tillett-Saks described a Progressive in Counterpunch, as one believing in a restrained free market, trade unions, taxing the wealthy, the nationalization of essential social needs such as education and healthcare, strong public welfare programs, higher minimum wage requirement and increased unionization, and the support of the poor.
The difference between a liberal and a progressive, at least as far as I see it; first I would extend the free market restraints to serious regulations on corporations. As far as taxing wealth, liberals have been way too lax on this in recent years. And liberals have been far too conceding on the establishment of private schools at the sake of the public school system. Bleeding liberals open welfare to the point of dispensing money without any control which I think is counterproductive. There hasn't been a sufficient drive in liberal politics to increase the minimum wage and to do more for the poor, both of which Progressives feel would improve the economy. And then there is my favorite of all, gun control, which some liberals even vote against.
Believe me, there are other differences that reside on an individual basis but the key factor here is that Progressives aren't saddled with a radical ideology like the Republican right. That's why we're called Progressives.