A mass noun, also known as a non-count noun, refers to something that cannot be counted individually. Instead of using numbers, mass nouns are quantified using terms like "some," "much," or "a little." Examples include substances like water, sand, and rice, which are seen as wholes rather than separate units. In contrast to count nouns, which can be pluralized (e.g., apple becomes apples), mass nouns remain singular. This distinction is important in grammar, as it affects verb agreement and article usage. For instance, we say "the water is cold" rather than "the waters are cold."