In grammar, the word plural denotes a quantity of more than one, in contrast to singular, which denotes a quantity of one. For example:
dos libros, cien libros, muchos libros - two books, one hundred books, many books
the word libros is plural, it is a plural noun
tres cajas, algunas cajas, varias cajas - three boxes, some boxes, several boxes
the word cajas is also a plural noun
Singular forms of these nouns would be libro (book) and reloj (watch), as in the following examples:
la caja - the box
The terms singular and plural are values of the grammatical category of number. Number affects nouns (as we have already seen above), pronouns, adjectives and verbs. Here are some simple examples of plural pronouns, adjectives and verbs:
Nosotros hablamos. - We speak.
Nosotros is a plural pronoun and hablamos is a plural verb.
Esas mujeres han cogido nuestras revistas. - Those women have taken our magazines.
Esas is a plural demonstrative adjective, han cogido is a plural verb and nuestras is a plural possessive adjective. Mujeres and revistas are plural nouns.
Todos mis sueños son buenos. - All my dreams are good.
Todos, mis and buenos are plural adjectives and son is a plural verb. Sueños is a plural noun.