What does an overpayment mean? and what it means to apply it to 2018?

[ddaven12]

If you have an overpayment it means you paid more taxes than you should have and you are getting a refund (money back). 

If you see a question that asks if you want to apply your overpayment to your next year's taxes, you want to say that you do not want to do that so that you will receive your full tax refund this year.