Gestation is the period of time when something is conceived and developed. The gestation period for human babies lasts nine months.
Gestation comes from the Latin gestare, which means to bear, or give birth to. We can talk about the gestation of fetus before it's born, but we also use gestation to talk about ideas. If you've been vaguely thinking about starting a revolution for the last year, then that idea has been in gestation.