Abstract expressionism | Tate https://www.tate.org.uk/art/art-terms/a/abstract-expressionism
Tate glossary definition for abstract expressionism: Term applied to new forms of abstract art developed by American painters in 1940s and 1950s, often characterized by gestural brush-strokes or mark-making, and the impression of spontaneity
Jackson Pollock and Willem de Kooning, who worked in a spontaneous improvisatory manner