From the Latin language, pico- is the correct term for 10^-12, as micro- is 10^-6, tera- is 10^+12, and, nano is 10^-9. Scientist and engineers use this convenient way to quickly and reliably take measurements of parameters relating to time, length (or area or volume), mass (or weight), temperatures, etc. It is very useful in avoiding the time-consuming process of writing out numbers, for example: 10^-21 written out would be: 0.000,000,000,000,000,000,001 ==> this can take a long time to write and/or type.