halo vs parhelic ring

halo and parhelic ring both are nouns.

Word	Noun	Adjective	Verb	Adverb
halo	Yes	No	No	No
parhelic ring	Yes	No	No	No

As nouns, parhelic ring is a hyponym of halo; that is, parhelic ring is a word with a more specific, narrower meaning than halo:

halo: a circle of light around the sun or moon
parhelic ring: a luminous halo parallel to the horizon at the altitude of the sun; caused by ice crystals in the atmosphere

Other hyponyms of halo include parhelic circle, solar halo.

halo (noun)	parhelic ring (noun)
an indication of radiant light drawn around the head of a saint	a luminous halo parallel to the horizon at the altitude of the sun; caused by ice crystals in the atmosphere
a circle of light around the sun or moon
a toroidal shape