The genitive case is a grammatical case used to indicate possession or a relationship between nouns. In English, it is often formed by adding an apostrophe and "s" to a noun, such as in the phrase "John's book," which shows that the book belongs to John. The genitive case can also be expressed using the preposition "of," as in "the cover of the book." In many languages, the genitive case has specific endings or forms that change based on the noun's gender, number, or case. For example, in Latin, the genitive singular of "puella" (girl) is "puellae," indicating possession, such as "the girl's dress." Understanding the genitive case helps clarify relationships between nouns in sentences.