earring vs drop earring

earring and drop earring both are nouns.

Word	Noun	Adjective	Verb	Adverb
earring	Yes	No	No	No
drop earring	Yes	No	No	No

As nouns, drop earring is a hyponym of earring; that is, drop earring is a word with a more specific, narrower meaning than earring:

earring: jewelry to ornament the ear; usually clipped to the earlobe or fastened through a hole in the lobe
drop earring: an earring with a pendant ornament

Other hyponyms of earring include eardrop, pendant earring, ear cuff, ear hook earring, ear wrap, earcuff.

earring (noun)	drop earring (noun)
jewelry to ornament the ear; usually clipped to the earlobe or fastened through a hole in the lobe	an earring with a pendant ornament