This is a good question, as the line between surrealism and absurdism is not always a clear one. This is particularly the case because they both fly in the face of any rational expression of an idea or concept. However, they have different goals. You can think of surrealism as an introspective examination and absurdism as more outward-looking.

Think of surrealism as an attempt to express notions and ideas that normally reside in one's subconscious. Surrealism is a means to explore concrete ideas through an irrational lens. For instance, Salvador Dalí, perhaps the quintessential surrealist artist, explores the concept of time in his famous painting Persistence of Memory, but not in a way that is concrete or realistic. Surrealism distorts reality in favor of the twists and turns that happen in the subconscious parts of our minds.

Absurdism, on the other hand, is more concerned with pointing out the irrationality of the universe itself. It favors chaos over order. Unlike surrealism, absurdism is not so much interested with notions of human thinking and the inner working of the mind. Instead, it aims to point out the futility in applying order in an orderless existence. An absurdist would argue that it is pointless to try to make order out of the chaos of existence. Therefore, it aims to point out that institutions such as religion, politics, and even society are ultimately pointless.