REM stands for Rapid Eye Movement, a unique phase of sleep characterized by quick movements of the eyes. During this stage, brain activity increases, resembling that of being awake, and most vivid dreams occur. REM sleep typically begins about 90 minutes after falling asleep and recurs several times throughout the night. This stage of sleep is essential for various functions, including memory consolidation and emotional regulation. Adults usually spend about 20-25% of their total sleep time in REM sleep, which is crucial for overall health and well-being. Lack of sufficient REM sleep can lead to cognitive and emotional issues.