According to the Merriam-Webster Dictionary, surrealism is

the principles, ideals, or practice of producing fantastic or incongruous imagery or effects in art, literature, film, or theater by means of unnatural or irrational juxtapositions and combinations.

In other words, surrealist artwork, writing, films, and theater tend to be unrealistic, illogical, disjointed, bizarre, and dreamlike. They often seem to be expressions of the unconscious.

As a cultural movement, surrealism began after World War I, possibly as a reaction to such horrific events as soldiers being mowed down by machine gun fire, chemical warfare, and the bombing of cities with large civilian populations. In the face of such chaos and horror, artists embraced the surreal.

The French poet Guillaume Apollinaire first used the term in 1917. In 1924, two writers with opposing viewpoints, Yvan Goll and Andre Breton, wrote works called the Surrealist Manifesto. Breton's work eventually exceeded Goll's in popularity and became the defining voice of surrealism.

Perhaps the most famous surrealistic painter was Salvador Dali. His evocative 1931 painting "The Persistence of Time," with its melting clocks in an austere landscape, has become iconically associated with the surrealist movement.