E layer vs E region

E layer and E region both are nouns.

Word	Noun	Adjective	Verb	Adverb
E layer	Yes	No	No	No
E region	Yes	No	No	No

As nouns, E layer and E region are synonyms defined as:

E layer and E region: a region of the ionosphere (from 50 to 90 miles up) that reflects radio waves of medium length

Other synonyms of E layer include Heaviside layer, Kennelly-Heaviside layer.

E layer (noun)	E region (noun)
a region of the ionosphere (from 50 to 90 miles up) that reflects radio waves of medium length	a region of the ionosphere (from 50 to 90 miles up) that reflects radio waves of medium length