The document discusses possessive nouns, which show ownership or belonging. It explains that singular possessive nouns are formed by adding an apostrophe and 's' to a singular noun (e.g. boy's). Plural possessive nouns are formed by adding only an apostrophe if the noun is plural (e.g. girls'), or by adding 's' if the noun is plural but does not end in s (e.g. mice's). Examples are provided to illustrate possessive nouns for both single and plural nouns.