Possessive nouns -- often formed by adding an apostrophe followed by an "s" to the end a word -- most commonly illustrate ownership. For example, in “Jenny’s shoes were left by the door,” the possessive “Jenny’s” reveals that the shoes belong to Jenny. Similarly, possessive nouns also demonstrate association, or relationship. For example,“ The company’s CEO retired yesterday.” Technically, the CEO does not belong to the company; rather, he is associated with the company.
Not limited merely to ownership and association, possessive nouns may express origin, description or a value of time. For example, “the President’s policies” reveal where the policies originated. The phrase “today’s sales” uses the possessive “today’s” to describe “sales.” To denote a value of time, “year’s” could be used to modify “salary,” as in “a year’s salary.”
Not all possessive nouns follow the apostrophe "s" convention. For example, "it's" with the apostrophe is the contraction for "it is," while "its" without an apostrophe is the possessive form. Proper nouns -- plural or singular -- like "Smiths" typically receive an apostrophe "s" to form the possessive. Common nouns already ending with an "s," however, usually receive an apostrophe only. For example, "girls" would be written as "girls'."