The suffix "-s" is commonly used in English to indicate the plural form of nouns. When you add "-s" to a singular noun, it signifies that there is more than one of that item. For example, the word cat becomes cats, meaning there are multiple cats. In some cases, nouns that end in certain letters may require different plural forms. For instance, nouns ending in s, x, z, ch, or sh typically take "-es" to form their plural, such as box becoming boxes. Understanding these rules helps in correctly using plural nouns in writing and speech.