One unusual modern use of the apostrophe is in plural acronyms, like“ICBM’s” “NGO’s” and “CD’s”. Since this pattern violates the rule thatapostrophes are not used before an S indicating a plural, many peopleobject to it. It is also perfectly legitimate to write “CDs,” etc. Seealso “.” But the use of apostrophes with initialisms like “learnyour ABC’s and “mind your P’s and Q’s” is now so universal as to beacceptable in almost any context.Note that “acronym” was used originally only to label pronounceableabbreviations like “NATO,” but is now generally applied to all sorts ofinitialisms. Be aware that some people consider this extended definitionof “acronym” to be an error.