ABC vs ABCs

ABC and ABCs both are nouns.

Word	Noun	Adjective	Verb	Adverb
ABC	Yes	No	No	No
ABCs	Yes	No	No	No

As nouns, ABC and ABCs are synonyms defined as:

ABC and ABCs: a character set that includes letters and is used to write a language

Other synonyms of ABC include ABC's, alphabet.

ABC (noun)	ABCs (noun)
a character set that includes letters and is used to write a language	a character set that includes letters and is used to write a language