peat bog vs quag

peat bog and quag both are nouns.

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

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

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
quag: a soft wet area of low-lying land that sinks underfoot

Other hyponyms of peat bog include mire, morass, quagmire, slack, slough.

peat bog (noun)	quag (noun)
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	a soft wet area of low-lying land that sinks underfoot