Suppose that I have submitted a job application. And now I am waiting for the result. Do I say "I am waiting for an answer from the company" or "I am waiting for the answer from the company" ?
Which article do I use?
Both are possible.
Using "an" is simply stating the fact, without it there would be a mistake in the sentence.
Using "the" will leave the impression that you know or believe that their will be an answer, either because this company always replies to everyone or because you have connections there and were told that they will respond or simply because you prefer to believe there will be one. The reason for that is that as a definite article "the" refers to something particular, something that we are familiar with.
Well, when it comes to such situation, this is what I've heard in common...
I'm waiting for their reply.
When you submit your resume, that's the better way to say because you did not ask anything to what they'd answer!
Still, let's consider that you want to use that sentence only. Then I'd prefer the.
I'm waiting for the answer.
The reason for that is you are waiting for an answer that is the reply to your job application and not anything else. It's not a reply in general. It's specific to your job application. You, yourself, used "I am waiting for the result!" Does not it answer the question? :)
Maybe, this is helpful to clarify it.
Yes, I also applied for the position and you know what, the reply was positive!
Here, the is used because that reply is unique to that application.