A dream is a sequence of sensations, images, emotions, and thoughts that occur involuntarily during sleep. Dreams are most vivid and memorable during REM (rapid eye movement) sleep, a phase of sleep characterized by intense brain activity, rapid eye movements, and temporary muscle paralysis that prevents the sleeper from acting out their dreams. The experience of dreaming is universal — virtually all humans dream, typically several times each night, though many dreams are not remembered upon waking. The content of dreams can range from mundane and realistic to highly abstract or fantastical, and can involve any combination of visual, auditory, emotional, and narrative elements. The purpose and meaning of dreams has been debated for centuries. Modern sleep science suggests that dreaming — particularly during REM sleep — plays an important role in emotional processing and memory consolidation. Dreams may help the brain process and integrate experiences, emotions, and information accumulated during the day, potentially contributing to problem-solving and creativity. Common types of dreams include ordinary narrative dreams, lucid dreams (in which the dreamer becomes aware that they are dreaming and may gain some control over the dream), nightmares (disturbing dreams that may cause the sleeper to wake), and recurring dreams (which repeat over time and may be linked to unresolved emotional themes). Dreams have held deep cultural, spiritual, and psychological significance throughout human history. While psychoanalytic theories proposed that dreams reveal hidden unconscious desires, contemporary neuroscience views dreaming primarily as a byproduct of the brain’s active processing during sleep.