A grammatical form used to talk about one person, thing etc.
Examples are: cat, dog, boy, girl, tree, book etc.
With an uncountable noun, the singular is usually the only form that exists at all.
Examples are: wheat, flour, water and spaghetti.
The grammatical category that distinguishes singular from plural is called number.
That form of a noun which normally denotes that more than one person or thing is being mentioned.
The English plural is regularly formed by adding -s (and sometimes -es) to the singular.
Examples are: boy/boys; girl/girls; book/books; fox/foxes.
A few dozen nouns form their plurals irregularly. Examples are: child/children; man/men; woman/women; tooth/teeth; foot/feet; millennium/millennia; and others.
Not all nouns have a plural form: for example, furniture, wheat, dust, news, advice and scenery normally have only a singular form. With some nouns, the plural is identical in form to the singular.
Examples are: sheep and deer.