term used to describe infants born before 37 weeks. Normal clinical gestation is 40 weeks (which is usually 36-38 weeks embryonic development) infants born after 42 weeks clinical gestation are called postmature. (More? Normal Development - Birth)
Happening, arriving, existing, or performed before the proper or usual time; adopted too soon; too early; untimely; as, a premature fall of snow; a premature birth; a premature opinion; premature decay.