-'s
/s after p/ /tkfor ɵ; əz after szʃʒʧor ʤ; z elsewhere/
noun suffix or pronoun suffix
used to form the possessive of singular nouns, of plural nouns not ending in s, of some pronouns, and of word groups that function as nouns or pronouns
The possessive of a plural noun that ends in s is formed by adding an apostrophe alone instead of 's.