DuckCorp Dico

Found one definition

1.                 From WordNet (r) 3.0 (2006):
                   
   
   
                   
                     
   REM
       n 1: a recurring sleep state during which dreaming occurs; a
            state of rapidly shifting eye movements during sleep [syn:
            paradoxical sleep, rapid eye movement sleep, REM
    sleep, rapid eye movement, REM]
       2: (Roentgen Equivalent Man) the dosage of ionizing radiation
          that will cause the same amount of injury to human tissue as
          1 roentgen of X-rays