Dreams are the manifestation of people's subconscious. When these consciousness are expressed, they will go through a series of steps such as combination, omission and modification. Finally, it presents a visual image, which is a dream. This process is called "dream processing"
Dream interpretation is the reverse process of this processing, which is equivalent to "dream translation". Infer the initial thoughts and attitudes of people's subconscious through the content of dreams.
Study hard, Interpretation of Dreams is a very interesting book.