A schedule with conditions that determines when stock options granted to employees will vest.
The conditions can be based on time, performance, or an event. In time-based vesting, options vest simply with the passage of time, i.e., as long as an employee continues in employment. In performance-based vesting, conditions mandate the employee to achieve certain targets for options to vest. In event-based vesting, vesting will depend on the occurrence of certain events, such as the company being listed for public trading, or becoming a unicorn, or becoming profitable.