ocean vs body of water

ocean and body of water both are nouns.

Word	Noun	Adjective	Verb	Adverb
ocean	Yes	No	No	No
body of water	Yes	No	No	No

As nouns, body of water is a hypernym of ocean; that is, body of water is a word with a broader meaning than ocean:

ocean: a large body of water constituting a principal part of the hydrosphere
body of water: the part of the earth's surface covered with water (such as a river or lake or ocean)

Other hypernyms of ocean include water.

ocean (noun)	body of water (noun)
a large body of water constituting a principal part of the hydrosphere	the part of the earth's surface covered with water (such as a river or lake or ocean)
anything apparently limitless in quantity or volume