We’ll try to explain it here in the easiest way possible. It’s hard to overestimate the importance of vesting. If you are a founder you need to get used to this concept as early as possible in your entrepreneurial career.
Otherwise, you may find yourself in a situation Mark Zuckerberg talks about: He didn’t know what vesting was at the point when he started the company, and it cost him billions of dollars because of his co-founder Eduardo Severin.
The notion of vesting comes from a legal universe. Vesting is a common provision in equity schemes. Vesting means receiving the right (to the shares of equity).
To put it simply, if founders agreed to divide equity with a vesting condition, what they get at the beginning is unvested equity, which is just a promise. A promise that they will get their shares of equity as agreed only if they certain vesting conditions are met. The most common vesting condition is to stay with the company long enough for the equity to vest. Vesting conditions may include various milestones important for the company. An example would be getting 1 mln. of registered users – if this happens, founders may agree to have accelerated vesting of 25% of their shares of equity.
Vested shares are the shares the founders already earned. Founders can walk away with those shares if they decide to leave the company. That will be fair, as they received those shares for all their hard work.
Vesting is important even for teams with unequal equity splits. In fact, vesting has little to do with equal or unequal splitting. Imagine there are three of you, you split your startup equity 45%-35%-20% and get to work. In a month a founder with 35% looses interest in the project and leaves… taking 35% with him! The other two work hard, get VC money, become famous and in 6 long years launch an IPO. Of course, over those years 35% get diluted to, say, 7%, but that’s 7% of a billion dollar company – not bad for a month of work, heh?
That’s a made-up example, of course, but if there were a vesting provision in place the founder who left in a month would get no equity. And this would be fair to those who stayed and made their company a huge success.