As to what is a billion, see above, but as to engineering (and scientific) terms there are a range of prefixes for example for the measurement of meters: 10^18 1Exemeter, 10^15 1 (I can't remember this one) 10^12 1 Terameter, 10^9 1 Gigameter, 10^6 1 Megameter, 10^3 1 Kilometer, 10^0 1 Meter, 10^-3, 1 milimeter, 10^-6 one micrometer, 10^-9 one nanometer, 10^-12 one picometer, 10^-15 one femptometer and 10^-18 one atometer. There are a range of other units, for exmaple a light year with is the distance traveled by light in onbe year, about 94.7 Terameters (I think) or an Anstrong 1^-10 meters or 0.1 nanometers. these terms are convenient for the scale the scientist/engineer is working at, but are also understandable by other workers in other fields and don't carry the ambiguity of 'a billion'. Hope this helps, Hamish