Plural is a grammatical number, typically referring to more than one of the referent in the real world.

In the English language, singular and plural are the only grammatical numbers.

In English, nouns, pronouns, and demonstratives inflect for plurality. (See English plural.) In many other languages, for example German and the various Romance languages, articles and adjectives also inflect for plurality. For example, in the English sentence "The brown cats are running", only the noun and verb are inflected; but in the German sentence "Die braunen Katzen rennen", every word (article, noun, adjective, and verb) is inflected.

In many languages, including a number of Indo-European languages, there is also a dual number (used for indicating two objects). Some other grammatical numbers present in various languages include trial (for three objects) and paucal (for a few objects). In languages with dual, trial, or paucal numbers, plural refers to numbers higher than those (i.e. more than two, more than three, or many). However, numbers besides singular, plural, and to a lesser extent dual, are extremely rare. Languages with measure words such as Chinese and Japanese lack any significant grammatical number at all, though they are likely to have plural personal pronouns.

Some languages distinguish between a plural and a greater plural. A greater plural refers to an abnormally large number for the object of discussion. It should also be noted that the distinction between the paucal, the plural, and the greater plural is often relative to the type of object under discussion. For example, for oranges the paucal number might imply less than ten, whereas for the population of a country it might be used for a few hundred thousand.

The Austronesian language Sursurunga has singular, dual, paucal, greater paucal, and plural. Lihir, another Austronesian language, has singular, dual, trial, paucal, and plural. These are probably the languages with the most complex grammatical number.

Languages having only a singular and plural form may still differ in their treatment of zero. For example, in English, German, Dutch, Italian, Spanish and Portuguese, the plural form is used for zero or more than one, and the singular for one thing only. By contrast, in French, the singular form is used for zero.

An interesting difference from Romance/Germanic languages is found in some Slavic and Baltic languages. Here, the final digits of the number determine its form. For example, Polish has singular and plural, and a special form (paucal) for numbers where the last digit is 2, 3 or 4, (excluding endings of 12, 13 and 14). In addition, Slovenian preserved pure dual, using it for numbers ending in 2. In Serbo-Croatian (in addition to the paucal for numbers 2-4), several nouns have alternate forms for counting plural and collective plural (the latter being treated as a collective noun). For example, there are two ways to say leaves: lišće (collective) is used in "Leaves are falling from the trees", but listovi (counting) is used in "Those are some beautiful leaves".