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.