town vs market town

town and market town both are nouns.

Word	Noun	Adjective	Verb	Adverb
town	Yes	No	No	No
market town	Yes	No	No	No

As nouns, market town is a hyponym of town; that is, market town is a word with a more specific, narrower meaning than town:

town: an urban area with a fixed boundary that is smaller than a city
market town: a (usually small) town where a public market is held at stated times

Other hyponyms of town include burg, boom town, cow town, cowtown, ghost town, hometown, Main Street.

town (noun)	market town (noun)
the people living in a municipality smaller than a city	a (usually small) town where a public market is held at stated times
an urban area with a fixed boundary that is smaller than a city
an administrative division of a county