an meaning:
one, or any
an sentence:
He is an active boy.
He is an honest man.
We had an oral exam.
I bought an old car.
A horse is an animal.
He made up an excuse.
I bought an old lamp.
He is just an amateur.
He is not an American.
He gave me an example.
He married an actress.
He is an army officer.
She is an office lady.
She is an early riser.
May I have an ice bag?
I have an old bicycle.
We rented an apartment.