SURREALISM 

Surrealism is an art that represent something in an excessive manner that tries to express the subconscious mind. It caters all forms, such as music, literature, philosophy, sculpture and especially in films. Therefore, Surrealism was a movement that played with the very means of representation. 

What are the things to be considered when a film is called surrealism? 

I think true surrealist film is experimental film, which means non-narrative and non-feature length film. A good example of surrealist film is Un Chien Andalou a 1921 film by Luis Buñuel.