n :  a state of deep usu. dreamless sleep that occurs regularly during a normal period of sleep with intervening periods of REM sleep and that is characterized by delta waves and a low level of autonomic physiological activity - called also non-REM sleep , NREM sleep , orthodox sleep , S sleep , synchronized sleep  .
 
 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.