...definite articles (def - i - nite art - ic -les)

"The" is the definite article.

"A" and "an" the indefinite articles.

The... pertains to that which is familiar or specific.

"A" or "an" when speaking in general.

Both the indefinite and definite articles are placed before a noun.

...Examples (ex - am - ple)

The dog just jumped over the fence.

A dog ran across the street.

Your ill, we need to see a doctor.

A woman entered the store.

We use "an" before any noun beginning with a vowel.

Would you like an apple or an orange?

An airoplane just landed in the field behind our house!  

vowels: a, e, i, o, and u.