The term 'Sleep Phases' refers to the different stages of sleep that a person goes through during the night. The acronym REMS stands for Rapid Eye Movement Sleep, which is one of the five stages of sleep. REMS is the stage of sleep when dreaming occurs and is the deepest stage of sleep. During this stage, the body is relaxed and the brain is active. Other sleep phases include light sleep, deep sleep, and ultra-deep sleep. All of these phases are important for a person's overall health and wellbeing.