A: Happy 40th Birthday!
B: I'm only 39! You're a year out.
In this case 'a year out' means the guess was wrong by one year.
A: I'm not going to university this year, I'm taking a year out.
In this case 'a year out' means the speaker is taking a break from something for a year.
Those are two just off the top of my head, there are quite a few other meanings. Like I said, when you use it in an example, we should be able to help more.
Student or Learner