Find out whether the underlined words in the given sentence is ‘definite’ or ‘indefinite’ articles:
This is a boring book.

The correct answer is: Indefinite

Indefinite articles are a, an (in the sense of 'one' or 'any') and the is a definite article (in the sense of 'this' and 'that'). An indefinite article 'a' is used before a consonant and 'an' is used before a vowel. Definite article 'the' is used when the speaker talks about a specific object.
'This is a boring book', here 'a' is an indefinite article.