alphabet vs character set

alphabet and character set both are nouns.

Word	Noun	Adjective	Verb	Adverb
alphabet	Yes	No	No	No
character set	Yes	No	No	No

As nouns, character set is a hypernym of alphabet; that is, character set is a word with a broader meaning than alphabet:

alphabet: a character set that includes letters and is used to write a language
character set: an ordered list of characters that are used together in writing or printing

Other hypernyms of alphabet include script.

alphabet (noun)	character set (noun)
the elementary stages of any subject (usually plural)	an ordered list of characters that are used together in writing or printing
a character set that includes letters and is used to write a language