ABC's vs character set

ABC's and character set both are nouns.

Word	Noun	Adjective	Verb	Adverb
ABC's	Yes	No	No	No
character set	Yes	No	No	No

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

ABC's: 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 ABC's include script.

ABC's (noun)	character set (noun)
a character set that includes letters and is used to write a language	an ordered list of characters that are used together in writing or printing