What was the meaning of "leftist" and "rightist" in those days?

Leftist avant-garde thinking, is inclined to reform and advocate social change in order to achieve progress, while the right is generally conservative forces, tend to be satisfied with the current state of affairs and do not advocate reform. The old generation of writers such as Guo Moruo is often called "famous left-wing writers" and so on.

Oh, I'm not a social or historical researcher, so I hope you'll correct me if I'm wrong.

I'm not a social or historical researcher.