Cliff
An initial period during which no equity vests, usually one year.
A cliff is the waiting period before any equity vests. On a standard four-year schedule with a one-year cliff, someone who leaves at eleven months takes nothing; at twelve months and one day, they take a quarter.
The cliff exists to filter out early departures. Hiring decisions are frequently wrong, and a year is roughly how long it takes to know.
Cliffs apply to founders too. It is one of the clearest signals to an investor that the founding team has thought seriously about what happens if the partnership does not work.