pico- [PEE koh]
(Italian: very small or from Spanish, "beak, tip, very small"; and from Latin, beccus, beak; also, a decimal prefix used in the international metric system for measurements)
This prefix is used in metric [decimal] system as trillionth [U.S.] and billionth part [U.K.], 10-12 [0.000 000 000 001]. The metric symbol for pico- is p.
In biomedicine, one pW is the average power consumption of a human cell; while 2.5 pW is the sound intensity per square centimeter for the average human threshold of hearing at 1000 Hz; and 150 pW is the power that enters a human eye from a 100 watt lamp one km away.