Benefits in a company retirement plan that are yours to keep if you leave the job. Your own contributions, to a 401(k), say, are immediately 100 percent vested. But employer contributions on your behalf can be vested gradually over a period of time, as a way to encourage you to stay with the employer. If you quit a job when just 50 percent of your benefits are vested, for example, you would forfeit half of the amount the employer has set aside for you.