Expressionism is really a general style of art, rather than a specific movement. It is an attitude or ethos about art’s ability to represent personal feelings and subjective experience rather than record lived reality with any representational accuracy.
The style is marked by distorted images that use strong outlines and bold colors. Compositions tend to be simpler and more direct, and are often characterized by thick impasto paint, loose freely applied brushstrokes, and occasional symbolism.
Definition adapted from Cork Art Encyclopedia, July 29, 2016