What it is:
A person is fully vested when a financial instrument or account becomes wholly owned by the investor.
How it works/Example:
Let's assume John Doe receives options to buy 2,000
His shares vest over a five-year period, meaning they do not become exercisable for five years. This means John must stay at the company for at least five years before he can exercise his stock options. After five years, he be fully vested.
Vesting is also common in retirement plans. For example, if John Doe's employer matches the contributions he makes to his retirement plan, those contributions might vest over, say, three years. This means that although the employer agrees to add extra, free to John's retirement account, that free money doesn't really become his for three years. Then he be fully vested.
Accelerated vesting occurs when a stock option becomes exercisable earlier than originally scheduled. So if Company ABC comes along and buys a 51% stake in Company XYZ, this constitutes a change in control and John Doe's options might automatically vest even though five years has not elapsed. John exercises his options at $10 a share, sells the shares for $20 a share, and walks away with a tidy profit.