ABC's vs ABC

ABC's and ABC both are nouns.

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

As nouns, ABC's and ABC are synonyms defined as:

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

Other synonyms of ABC's include ABCs, alphabet.

ABC's (noun)	ABC (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