Number.
When we speak of a single thing, we use what is called the Singular form.
E.g.: Horse, man, party …
When we speak of more than one of anything, we use what is called the Plural form.
E.g. Horses, men, parties …
Generally, only Common nouns and Collective nouns are used in the plural.
Material nouns, Proper nouns and Abstract nouns are used in the plural, only when they are used as Common nouns.
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