DVD vs optical disk

DVD and optical disk both are nouns.

Word	Noun	Adjective	Verb	Adverb
DVD	Yes	No	No	No
optical disk	Yes	No	No	No

As nouns, optical disk is a hypernym of DVD; that is, optical disk is a word with a broader meaning than DVD:

DVD: a digital recording (as of a movie) on an optical disk that can be played on a computer or a television set
optical disk: a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface

Other hypernyms of DVD include optical disc.

DVD (noun)	optical disk (noun)
a digital recording (as of a movie) on an optical disk that can be played on a computer or a television set	a disk coated with plastic that can store digital data as tiny pits etched in the surface; is read with a laser that scans the surface