E region vs E layer

E region and E layer both are nouns.

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

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

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

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

E region (noun)	E layer (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