fashion vs high fashion

fashion and high fashion both are nouns.

Word	Noun	Adjective	Verb	Adverb
fashion	Yes	No	Yes	No
high fashion	Yes	No	No	No

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

fashion: the latest and most admired style in clothes and cosmetics and behavior
high fashion: trend-setting fashions

Other hyponyms of fashion include cult of personality, cut, haute couture, high style, craze, cult, fad, furor, furore, rage, retro.

fashion (noun)	high fashion (noun)
characteristic or habitual practice	trend-setting fashions
consumer goods (especially clothing) in the current mode
how something is done or how it happens
the latest and most admired style in clothes and cosmetics and behavior

fashion (verb)	high fashion (verb)
make out of components (often in an improvising manner)