Also: Simple Agreement for Future Equity
An investment contract where money goes in now and converts to shares later, at the terms of a future priced round.
Created by Y Combinator to avoid negotiating a valuation before a company has enough evidence to argue one. The investor wires money today; what percentage they end up owning is settled at the next priced round, adjusted by whatever cap and discount the SAFE specifies.
The thing first-time founders miss is that SAFEs stack. Each one is easy to sign in isolation, and none of them shows up on the cap table until they convert — so the dilution is invisible until the day it all lands at once. Model the conversion before signing the second one, not after the fourth.
Also note the post-money variant, which is now the common form: it fixes the investor's percentage of the company rather than a pre-money valuation, meaning subsequent SAFEs dilute you rather than them.
Project types where this term stops being vocabulary and starts being a decision you have to make.