The term “action painting” was coined in the 1940s by an American art critic named Harold Rosenburg. He thought canvases were arenas where violent acts were committed and should be allowed. A more, uh, legal way than other ways. This kind of painting is also called gestural painting.
This form of painting involves globbing and caking on paint so thickly that one could see the brush strokes in the finished painting. Franz Kline and Jackson Pollock are two of the most well-known action painters. This is because the form puts the act of creating art above the finished product itself, and how the finished product looked. It’s supposed to represent, at least according to the painters who do it, the act of creating art instead of a specific model or landscape.