The time at which a right to purchase securities becomes unconditional. Over a period of time an employee of a company earns rights to receive benefits (e.g., stock) as a result of that employment, though until the rights are earned the employee may not be able to claim ownership of the related benefits and those potential benefits are forfeitable. Restricted stock or options, or warrants to purchase stock that may not be sold or exercised, or that are subject to risk of forfeiture for a period of time, are 'unvested'. That portion of the stock that is not subject to risk of forfeiture and that may be sold, or the options and warrants that may be exercised, are referred to as 'vested'.