The term “progressivism” can be used in many different ways, depending on the context and on who is speaking. Since you have put this question in the history group, I will assume that you are asking about progressivism in the context of American history. In that case, “progressivism” refers to a set of middle-class, reformist ideas that were espoused by the Progressives, most notably in the first two decades of the 20th century.
The Progressives were mainly dedicated to the idea that the government should enact various reforms. Progressivism was a set of ideas that wanted the government to enact laws that would reduce the powers of the rich elites while also improving the morals of society as a whole. It also envisioned private individuals and groups taking actions to improve social values.
Progressivism, then, wanted laws like antitrust laws and workplace safety laws to prevent rich elites from abusing those with less money. They wanted direct election of senators to prevent the rich from using their money to corrupt the political system. They wanted Prohibition to improve social morals. At the same time, they wanted private initiatives such as the settlement house movement to help improve social values and conditions as well.
Thus, “progressivism” was a philosophy that wanted the government (and individuals) to work to reduce the power of the rich and to improve social values and morals.