An article is a determiner used to show that we know specifically which thing or things being are referred to (the definite article) or that we don't know the thing being referred to (indefinite article). They are also used to talk about particular things or things in general.
Unlike some other Western European languages, there is only one definite article in English: the. It can be used to refer to singular (the book) or plural (the books). 'The' is also the commonest written word in the English language.
There are two indefinite articles in English: a and an. They are both singular in meaning. The words some and any can be used as the plural forms of a/an.
See zero article.