wetland vs peat bog

wetland and peat bog both are nouns.

Word	Noun	Adjective	Verb	Adverb
wetland	Yes	No	No	No
peat bog	Yes	No	No	No

As nouns, peat bog is a hyponym of wetland; that is, peat bog is a word with a more specific, narrower meaning than wetland:

wetland: a low area where the land is saturated with water
peat bog: wet spongy ground of decomposing vegetation; has poorer drainage than a swamp; soil is unfit for cultivation but can be cut and dried and used for fuel

Other hyponyms of wetland include bog, fen, fenland, marsh, marshland, swamp, swampland.

wetland (noun)	peat bog (noun)
a low area where the land is saturated with water	wet spongy ground of decomposing vegetation; has poorer drainage than a swamp; soil is unfit for cultivation but can be cut and dried and used for fuel