The plural is one of the categories of grammatical number in many languages. Plural forms of nouns typically denote a quantity other than the default quantity represented by a noun, which is generally one (the form that represents this default quantity is said to be of singular number). Most commonly, therefore, plurals are used to denote two or more of something, although they may also denote fractional, zero or negative amounts. An example of a plural is the English word cats, which is derived from the singular cat.
Plurality is a linguistic universal, represented variously among the languages as a separate word (free morpheme), an affix (bound morpheme), or by other morphological indications such as stress or implicit markers/context.
Words of other types, such as verbs, adjectives and pronouns, also frequently have distinct plural forms, which are used in agreement with the number of their associated nouns.
Some languages also have a dual (denoting exactly two of something) or other systems of number categories. However in English and many other languages, singular and plural are the only grammatical numbers, except for possible remnants of the dual in pronouns such as both and either.
Read more about Plural: The Plural Within Systems of Grammatical Number, Formation of Plurals, Plural Forms of Other Parts of Speech, Nouns Lacking Plural or Singular Form, Usage of The Plural, POS Tagging