Countable and Uncountable Nouns
Countable nouns are things we can count, like apples. Uncountable nouns are things we can't count, like air.
Countable nouns are used to name things we can count.
Four boys, etc.
Countable nouns have a singular and a plural form.
The article 'A' is used with a noun that begins with a consonant, and the article 'An' is used with a noun that begins with a vowel sound.
Uncountable nouns are used to name things we can not count:
Money (we can count dollars, euros, but not money)
Uncountable nouns do not usually take the indefinite article 'A' or 'An'. They are often used without an article and they do not usually have a plural form.
Some words can be countable and uncountable, depending on what they refer to. For example, 'Hair'.
Paul has brown hair. (This refers to his hair in general and is uncountable)
There is a hair in my dinner. (This refers to individual hairs, and is countable)