Here's why:
* Indefinite: They don't refer to a specific noun. They simply indicate that the noun is one of a general class.
* Articles: They are words that precede nouns, often indicating whether the noun is singular or plural, and whether it's definite (specific) or indefinite (general).
Examples:
* A cat (any cat)
* An apple (any apple)
* The cat (a specific cat)
* The apples (a specific group of apples)