rapid eye movement sleep vs REM

rapid eye movement sleep and REM both are nouns.

Word	Noun	Adjective	Verb	Adverb
rapid eye movement sleep	Yes	No	No	No
REM	Yes	No	No	No

As nouns, rapid eye movement sleep and REM are synonyms defined as:

rapid eye movement sleep and REM: a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep

Other synonyms of rapid eye movement sleep include paradoxical sleep, rapid eye movement, REM sleep.

rapid eye movement sleep (noun)	REM (noun)
a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep	a recurring sleep state during which dreaming occurs; a state of rapidly shifting eye movements during sleep