It means that if you quit, you get to take all of your retirement funds with you.
At my last job, it took 5 years to vest. Usually your company contributes to your 401k, but you don't have 100% of those funds until you are vested. SO if I left that old job at 4 years, I got like 80% of the funds they contributed. I believe I was still entitled to 100% of anything *I* put in.
