Three words ‘a’ ‘an’ and ‘the’ are called
articles.

Articles are of two types:

1. Indefinite Articles
2. Definite articles

1. Indefinite Articles – ‘A’ and ‘An’ are weakened form of one and are
   called Indefinite Articles as they do not point out to any particular person or
   thing.
2. Definite article – ‘The’ is called the definite article because it points out some definite
   or particular person or thing.

Use of Indefinite articles ‘A’
and ‘An’:

Use of indefinite article ‘A’;

• Before a word beginning with a consonant sound:

A boy, a pen

• Before a word beginning with the sound ‘yu’

A
university, a union, a unicorn, a usage, a
European, a unicorn

• Before a word beginning with the sound ‘wu’

A one-pound
note, a one-eyed…