Number refers to whether a noun is singular or plural based on its meaning. Singular nouns relate to one entity or item, while plural nouns relate to two or more entities or items. There are several classifications of nouns according to their number, including regular nouns that form plurals by adding -s, irregular nouns that change spelling or form for plurals, and special classes of nouns like collective nouns, binary nouns, and pluralia tantum nouns that are always plural in form regardless of number. Proper nouns, noncount nouns, and abstract nouns are usually singular.

1. NUMBER

2.  Number is a grammatical category that
requires a noun to be understood
grammatically as either singular or plural.
 Singular relates to the quantity “one” for
count nouns, to the unique referent for most
proper nouns and to undifferentiated mass
for uncountable nouns.
 Plural relates to the quantity “two or more”
for count nouns, to the unique referent for
some proper nouns and to individual units
that are seen as reflecting plural
composition.

3. Classification of nouns according to Number
(Randolph Quirk)

4.  REGULAR SPELLING

5.  Irregular spelling

7.  Ordinarily Singular nouns.
Noncount nouns,abstract nouns and proper
nouns are singular and invariable.
Nouns ending in –ics denoting subjects,
sciences are usually invariable and treated as
singular, however, some can be singular or
plural when such words denote one´s
knowledge of the subject.

8. Names of diseases

9. Names of some games ending in -s

10. Abstract adjective heads
Collective nouns: a collection of people or
things considered together and spoken as a
whole.

11. Summation plural or Binary nouns: denote
tools, instruments and articles of dress
consisting ot two equal parts which are
joined together.

12. Pluralia Tantum or Aggregate nouns
ending in –s, refer to entities comprising an
indefinite number of parts.

13. Unmarked plural nouns: these nouns
have no plural form but are used as plurals.

14. Personal adjective heads and nationalities
adjectives take plural verb.

15. Summing it up