In English grammar, nouns are frequently categorized based on their ability to be counted as separate units or not. Countable nouns can generally appear in both singular and plural forms, and they can be modified by numbers. They are often preceded by articles such as "a" or "an" when referring to a single item. Uncountable nouns, conversely, do not usually take plural forms and cannot be paired directly with numbers in standard usage. Choose the one that is traditionally regarded as an uncountable noun in English: