According to the Encyclopedia Britannica, in the metric system the prefix "milli" is used to designate one-thousandth of a unit. A common example would be a millimeter, which is equal to one-thousandth of a meter.
The prefixes used in the metric system are based on multiples of ten. One-hundreth of a unit is prefixed with "centi," one-tenth is "deci," ten is "deca," one hundred is "hecto" and one thousand is "kilo," as in kilometer.
Some other prefixes to note include "mega" (one million) and "giga" (one billion) which are recognizable from the computer units megabyte and gigabyte.
"Nano," meaning one-billionth, is the prefix used in referring to nanotechnology.