In grammar, articles are words that come before a noun to indicate whether the noun is specific or general. In English, there are three articles: the, a, and an.

• Definite article: The definite article is "the" and is used before a noun to indicate that the identity of the noun is known to the reader. It is used to refer to specific or particular nouns. For example, "the book" refers to a specific book.

• Indefinite article: The indefinite article takes two forms: "a" and "an". It is used before a noun that is general or when its identity is not known. For example, "a book" refers to any book rather than a specific book.

• Zero article: In some cases, no article is used before a noun. This occurs with plural and uncountable nouns when they are used in a general sense. For example, "I love dogs" or "I need water."

Articles are a type of adjective and modify nouns. They can also modify anything that acts as a noun, such as a pronoun or a noun phrase. The choice of article depends on whether the noun is specific or general, and whether it is countable or uncountable.