What are definite and indefinite articles?

Articles are words which tell us whether a noun is general (any noun) or specific. There are three articles:
 

1. the (specific or definite)
2. a (general or indefinite)
3. an (general or indefinite when followed by a noun which begins with a vowel)

For example:

The indefinite article 'a' (in red) tells us that the person who wrote the sentence was seeing the cat for the first time.

In this sentence:

The definite article 'the' (in red) tells us that this was a cat that had been seen before, or was known by the person writing the sentence.

Often, in a story, a person or thing will be introduced using the indefinite article and then afterwards will be referred to with the definite article. For example:

First, 'a witch' is used because the witch has not been seen before. Then 'the witch' is used because she has already been introduced and can therefore be referred to with the definite article.

Articles are determiners, words which come at the beginning of the noun phrase and tell us whether the noun phrase is specific or general. According to the primary curriculum, revised in 2014, children should be taught correct grammatical terminology, so they will learn that articles are one of many different kinds of determiners.