In grammar, the term number refers to the way in which differences between singular and plural are shown grammatically.
An English noun exhibits a two-way distinction of number: a singular form, denoting one of something, and a plural form, denoting two or more.
The singular form has no particular marking, while the plural form carries the suffix –s or –es.
Examples are: boy/boys; book/books; tree/trees; pen/pens; car/cars; box/boxes.
A few dozen nouns form their plurals irregularly. Examples are: child/children; man/men; woman/women; foot/feet; tooth/teeth; mouse/mice; radius/radii.
Some nouns are unusual in having only a singular form or only a plural form. Nouns which have only a singular form include furniture, wheat, happiness, gratitude, knitting and rugby. Nouns which have only a plural form include police, cattle, oats, tweezers, pants and remains