The possessive case is a grammatical form used to indicate ownership or association. There are several synonyms for the possessive case, including genitive case, s-genitive, and possessive inflection. In English, the possessive case is typically formed by adding an apostrophe (') and the letter "s" to the end of the noun. For example, "John's book" indicates that the book belongs to John. However, some nouns that end in "s" only require an apostrophe. For example, "the girls' room" indicates that the room belongs to the girls. Different languages have different ways of indicating the possessive case, often using different suffixes or word order.