bifocals vs eyeglasses

bifocals and eyeglasses both are nouns.

Word	Noun	Adjective	Verb	Adverb
bifocals	Yes	No	No	No
eyeglasses	Yes	No	No	No

As nouns, eyeglasses is a hypernym of bifocals; that is, eyeglasses is a word with a broader meaning than bifocals:

bifocals: (plural) eyeglasses having two focal lengths, one for near vision and the other for far vision
eyeglasses: (plural) optical instrument consisting of a frame that holds a pair of lenses for correcting defective vision

Other hypernyms of bifocals include glasses, specs, spectacles.

bifocals (noun)	eyeglasses (noun)
(plural) eyeglasses having two focal lengths, one for near vision and the other for far vision	(plural) optical instrument consisting of a frame that holds a pair of lenses for correcting defective vision