Meaning of -'S in English

noun suffix or pronoun suffix Etymology: Middle English -es, -s, genitive singular ending, from Old English -es; akin to Old High German -es, genitive singular ending, Greek -oio, -ou, Sanskrit -asya — used to form the possessive of singular nouns , of plural nouns not ending in s , of some pronouns , and of word groups functioning as nouns or pronouns

Merriam Webster. Explanatory English dictionary Merriam Webster.      Толковый словарь английского языка Мерриам-Уэбстер.