character set vs ABCs

character set and ABCs both are nouns.

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

As nouns, ABCs is a hyponym of character set; that is, ABCs is a word with a more specific, narrower meaning than character set:

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

Other hyponyms of character set include ABC's, ABC, alphabet, alphanumeric characters, alphanumerics.

character set (noun)	ABCs (noun)
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