4 years with a 1-year cliff describes a common vesting schedule that startups use. Translated, this means that a startup employee who has been granted equity subject to this vesting schedule would vest 25% of their equity after 1 year (the cliff), and would vest the remaining 75% of their equity over the next 3 years, assuming the service provider stays with the startup the entire time. The end result after 4 years of continuous service is that the employee would be fully vested.
Explore the complexities of startup equity vesting, especially when an acquisition occurs. Understand the function and uses for accelerated vesting like single-trigger and double-trigger acceleration.