It's either what Tbone said, or just the opposite. One is when you met your commitment and the other is when you still owe some. I think Tbone is correct in that chase is when you are needing a waiver to get out, and you spend a lot of time chasing your tail to get it.

Front is basically you getting into the reserves/ang before you get off active duty.

I would not bet on which was which though...