Short answers, pulled from the story.
Expressionism is a modernist movement that began in poetry and painting in Northern Europe around the start of the 20th century. It presents the world solely from a subjective perspective, distorting it radically for emotional effect to evoke moods or ideas rather than physical reality.
Expressionism originated principally in Germany and Austria around the beginning of the 20th century. It developed as an avant-garde style before the First World War and remained popular during the Weimar Republic, particularly in Berlin.
The two main groups were Die Brucke, the Bridge, formed in Dresden in 1905 and led by Ernst Ludwig Kirchner, and Der Blaue Reiter, the Blue Rider, formed in Munich in 1911. The Blue Rider included Wassily Kandinsky, Franz Marc, Paul Klee, and August Macke.
Key Expressionist films from German cinema include Robert Wiene's The Cabinet of Dr. Caligari from 1920, Paul Wegener's The Golem from 1920, F. W. Murnau's Nosferatu from 1922, and Fritz Lang's Metropolis from 1927. The style relied on distorted set design, chiaroscuro lighting, and distorted camera angles.
The term expressionism was probably first applied to music in 1918, especially to Arnold Schoenberg, who avoided traditional forms of beauty to convey powerful feelings. Schoenberg, Anton Webern, and Alban Berg formed the Second Viennese School, and Theodor Adorno wrote that the depiction of fear lies at the centre of expressionist music.
Expressionism is difficult to define partly because it overlapped with other movements like Futurism, Vorticism, Cubism, Surrealism, and Dadaism. Richard Murphy notes that some of its most challenging figures, such as Kafka, Gottfried Benn, and Doblin, were simultaneously the most vociferous anti-expressionists.